COLORADO

GEOLO G I C A L S URVEY

COLORADO GEOLOGICAL SURVEY

Department of Natural Resources

1313 ShermanStreet, Room 715Denver, CO 80203

PH: (303) 866-2611FAX: (303) 866-2461

November 1998

CONTENTS

✦ Solving Land-Use Problems Using the Colorado Geological Survey...1

✦ Assessment of Geologic Suitability of Colorado LandSubdivision—25 Years’ Experience...3

✦ Avalanche Facts...11✦ Coalbed Methane—A Potential Geologic Hazard...13✦ Geologic Hazard Reviews Performed by the

Colorado Geological Survey...16✦ School-Site Reviews...18✦ CGS Fee Schedule...19

COLORADOGEOLOGICAL SURVEY

Solving Land-UseProblems

HISTORY AND EXPERIENCEFor over two decades, the Colo-rado Geological Survey (CGS)has assisted Colorado countygovernments with geologic-hazard problems and other geo-logic concerns related to pro-posed land-use changes. Initially,most of the cases were for resi-dential subdivisions in unincor-porated areas. Senate Bill 35(1972) directs CGS to review andreport on these to the Boards ofCounty Commissioners throughtheir planning departments. Inrecent years, this function hasevolved into a wide range ofland-use reviews and environ-mental studies. These services arealso frequently provided, at theirrequest, to municipalities andother entities.

HOUSINGCurrently, the services that theCGS offers to Counties usuallyfocus on county planners and,indirectly, building officials whohave responsibility for thereasonable safety and feasibilityof new housing construction.CGS services include geologicaland geotechnical reviews of site-investigation documents whichare supplied by the developer fora proposed subdivision. The ulti-mate customers are elected offi-cials who make the actual land-use decisions and policies. Thetopography, rocks, and soils ofour State can present extremelydifficult design and construction

problems and if these are notconsidered adequately in plan-ning, engineering, and construc-tion, the citizen homeowner caneventually be presented withmaintenance problems for hisresidence that are costly or evenimpossible to solve.

INFRASTRUCTUREThe serviceability of the publicinfrastructure can be drasticallyaffected by adverse geologic con-ditions too. Road alignments andconstruction,water-supply andwater-treatment facility sitingand expansions, school-siteacquisition and school-facilityconstruction (H.B. 1045, 1984),and landfill and mine locationsare several of the kinds of caseswith which the Survey has devel-oped experience over many years.

Sometimes, such cases involvecontroversy and, by makingobjective investigations and real-istic reviews for public officials,the decisions can be made usingrelevant geologic facts. This canbe important to public confidencein local government even whenan adversarial, fractious atmos-phere is prevalent, as is frequent-ly the case with gravel pits,mines, quarries, and landfills.

PLANNING To improve land-use planning,the Survey can conduct topicalstudies of geologic conditionsand processes. Examples of espe-cially problematical and costly-

to-mitigate geologic hazards are expansive, heaving, settling,and corrosive soils, rapid massmovements such as rockfalls anddebris flows, and large-scalelandslides in developing moun-tainous areas or critical trans-portation and utility corridors.Interpretive, intermediate- tolarge-scale geologic mapping andinvestigations of soils andbedrock, when appropriately formatted, can be used by plan-ners and developers to identifypotential geology-related prob-lems early in the process.

The Survey has workedrecently with Jefferson and Douglas Counties (see sectionbelow titled “Working WithCounties. . .”) to study soil-related problems which have costhomeowners and local govern-ments millions of dollars. Otherrecent cases include ongoingstudies of landslides at theDowd’s Junction infrastructure-complex corridor west of Vail,assistance to the City of GrandJunction with a subdivision areaon a landslide immediately abovethe Colorado River, monitoringof the continuing debris-flowthreats to the I-70 corridor fromthe 1994 Storm King Mountainburn area, and the Town of Vailwith mitigation of severe rockfallhazards near Booth Creek.

ENVIRONMENTWith the advent of new State andFederal environmental laws and

1

SOLVING LAND-USE PROBLEMSUSING THE

COLORADO GEOLOGICAL SURVEY

SOLVING LAND-USE PROBLEMSUSING THE

COLORADO GEOLOGICAL SURVEY

regulations, the Survey now worksfor the Colorado Department ofTransportation and other Stateagencies in site investigationsand remediations of under-ground-storage-tank sites. TheU.S. Forest Service is benefitingfrom the Survey’s inventory andassessment of environmental andground-water degradations andhazardous mine openings causedby past mining and other activi-ties on lands under its jurisdiction.

GEOGRAPHIC INFORMATION SYSTEMSOne of the greatest challenges ofland use planning is that of com-piling and comparing all relevantinformation about an area andmaking an informed decisionabout how that area should bemanaged. This requires assem-bling a variety of dissimilar setsof information and synthesizingthem into a usable form.

For the last ten years, CGShas utilized computer-based tech-nologies to help Colorado gov-ernments resolve land-use issueswhich have geologic problemsand concerns. More recently,Geographic Information System(GIS) technologies have becomeavailable which greatly enhanceour ability to provide decisionsupport to county and local gov-ernments on these issues. Also,CGS now manages a GIS libraryof digital geologic and geo-graphic data which, when com-bined with county and local-government data sets, can beused to better understand the fullrange of factors affecting an areaof concern. This GIS technologyallows scientists, in partnershipwith government decision-makers, to integrate a wide vari-ety of information into a unifiedform and helps to visualize vari-ous combinations of data to gain

a better understanding of the potential impacts of land usedecisions.

WORKING WITH COUNTIES:RECENT EXAMPLES OFCGS LAND-USE-PLANNING ASSISTANCEA belt of land along the centralFront Range foothills in Coloradois experiencing tremendous pop-ulation growth, but has beenbeset with problems due to thepost-construction development ofa distinctive type of groundheave. The ground deformationsassume the form of low, linearmounds and have caused mil-lions of dollars in property dam-age to houses, commercial build-ings, roadways and utility lines.Early attempts to solve the prob-lem using conventional engineer-ing technology were largelyunsuccessful.

The Colorado Geological Sur-vey has assumed a leading rolein determining that this costlyproblem is clearly and funda-mentally geologic and has under-taken steps to assist planningagencies in Jefferson and DouglasCounties to deal with the prob-lem according to the particularneeds of each county.

In Jefferson County, suburbangrowth in the affected area hasoccurred for nearly two decadesand continues to this day. Basedon the high demand for homes inthis area, it is unlikely that actualgrowth will be discouraged. TheCGS and Jefferson County haveworked cooperatively to studythe causes and areal extent ofheaving ground at selected re-search sites in the County. Coun-ty officials and staff have beeninformed of the presence, magni-tude, and nature of the problemduring a series of CGS-led fieldtrips which visited impacted

areas. Finally, CGS geologistschaired two subcommittees of theJefferson County Expansive SoilsTask Force in 1994. The TaskForce delineated an overlay dis-trict of potentially heavingground and developed a compre-hensive set of amendments to theland-development regulations forexplicitly recognizing and miti-gating problem areas. The over-lay-district map was created forthe County in digital form by theCGS using a Geographic Inform-ation System (GIS) format whichis fully compatible with its otherexisting GIS-mapping and plan-ning functions.

Douglas County, in contrast,has seen only limited develop-ment within its Front Rangefoothills area. However, verycostly damage has occurred thereand the pressure to develop thearea is extreme. The County is inan advantageous position tomodify its long-range planninggoals for this area because somuch land remains unplatted.The CGS was contracted by Douglas County to delineate ageology-specific overlay districtmap (Special Publication 42),again using a GIS digital format,and to consider recommenda-tions for future prudent land usein the area of potentially heavingbedrock, including creative delin-eation of areas which may beconsidered for low-impact usesuch as open space.

In both counties, the Colora-do Geological Survey continuesto be active in reviewing pro-posed subdivisions which arelocated within the overlay dis-tricts to help ensure that futurehomeowners, and county agen-cies, will not be exposed toundue financial or safety risksfrom heaving-ground hazards.

2

ABSTRACTSince 1972, when the enablingColorado statute was enacted, theColorado Geological Survey(CGS) has reviewed requiredengineering geologic reports forsubdivisions prepared for countyplanning departments by privateconsultants. These consultants areretained by subdividers of unin-corporated land who proposeparcels of 35 acres or less. CGS’role is to advise county officials about report adequacy inindicating potentially adversegeologic conditions. Regardless ofour findings, the final decisionabout acceptance of a submittedreport is always made by a countygovernment.

The majority of these subdivi-sions are residential and manyare for “recreational homes” inremote, mountainous localities.CGS has been placed in a similarrole by municipalities for caseswhere reviews have been volun-tarily requested. Several hundredreviews are done annuallystatewide. Review activity hasreflected mountain development,usually in skiing or all-seasonresorts, economic and populationgrowth along the Front Rangeand established smaller commu-nities throughout the State, andenergy-resource-development-related growth in western Colora-do. During the nineties, virtuallyall of Colorado has seen econ-omic and population growth andthis is reflected in the review

activity. Some of the reviews havecorroborated consultants’ recom-mendations entirely; others haveindicated where additional studyand remedial-engineering workneeded to be done; and a fewhave demonstrated the nearlycomplete technical and/or economic infeasibility of a land-development proposal.

This discussion is about thegeneral background of CGSinvolvement with geologic haz-ards in land subdivisions and,mostly without citing specificcases, some of our experiences inevaluating the adequacy of geo-technical reports. In many cases,monetary savings and/or reduc-tion in likelihood of future engi-neering-performance and safetyproblems have been realized.

INTRODUCTIONShortly after its reestablishmentin 1969, and coincident with aperiod of rapid economic andpopulation growth in Colorado,the fledgling Colorado GeologicalSurvey (CGS) became involvedwith geotechnical problemscaused by land development. Theearliest, and then very innova-tive, published work which wasused by the CGS to convey geo-logic information to county land-use planners was that of Gardnerand Hart (1971) for the Golden7.5-minute quadrangle (westDenver metropolitan area-Figure1, Locality 1). Subsequently,Rogers and Rold (1972) studied

the serious and practically insur-mountable geologic-hazard prob-lems that could have been causedby proposed development of the,now defunct, destination ski-areacomplex at Marble, GunnisonCounty (Locality 2).

This involvement with geo-logic-hazards continues to thepresent and was mandated for-mally by legislation in 1972 (Sen-ate Bill 35). House Bill 1041 (1974)was enacted and the CGSresponded with legal definitionsof geologic hazards and guide-lines for investigation of them(Rogers and others, 1974). Thislegislation also instructed coun-ties that the geologic hazardsdefined and discussed therein are“matters of State interest” and tobetter facilitate safe land develop-ment in geologic-hazard areas,mapping of these hazard areasshould commence and that theState would offer technical sup-port for the work.

The CGS and several privatecontractors initiated numerouspilot mapping programs and top-ical studies to respond to thisdirective (Amuedo and Ivey,1975; Kirkham and Rogers, 1981;Mears, 1976; Soule, 1976; Soule,1978). Some counties, such asEagle (Vail-Locality 3), contractedwith private consultant(s) toundertake hazards-mappingwork (Robinson and Associates,1975). Costa and Bilodeau (1982,p. 309–310) outline the back-ground of engineering-geologic

3

ASSESSMENT OF GEOLOGIC SUITABLIITYOF COLORADO SUBDIVISIONS—

25 YEARS’ EXPERIENCEBY JAMES M. SOULE

ASSESSMENT OF GEOLOGIC SUITABLIITYOF COLORADO SUBDIVISIONS—

25 YEARS’ EXPERIENCEBY JAMES M. SOULE

practice in Colorado during thattime and scientific, legal andadministrative aspects of this lawand its implementation are dis-cussed in Shelton (1977). Basedmostly on Colorado experiences,Soule (1980) discusses some ofthe technical problems andsemantic pitfalls of engineering-geologic mapping of geologichazards.

Colorado can be grosslydivided into three physiographicprovinces (Figure 1), each withcharacteristic geologic environ-ment(s) and physical propertiesof its soils and rocks. Theseprovinces are the high plainsand piedmont east of the centralRocky Mountains front whereCretaceous and Cenozoic sedi-mentary rocks and a suite of late

Tertiary to Holocene alluviumsand eolian deposits predomi-nate; the central Rocky Moun-tains themselves where Precam-brian to Tertiary igneous andmetamorphic rocks, Cretaceousto Tertiary sedimentary rocks,and their derived colluviumsand alluviums are most com-mon; and the table lands andplateaus of western Coloradowhere nearly flat-lying, but com-monly deeply dissected, Creta-ceous to Tertiary sedimentaryrocks dominate the terrain.Alpine glacial deposits occur inthe higher mountains and largescale mass wasting (landsliding)of many different kinds of mate-rials occurred during the Neo-gene to late Pleistocene and/orHolocene on the side slopes of

many mountains and plateaus.Unstable slopes (landslides of

all types and landslide-proneground) and expansive soils androck are probably Colorado’smost widespread geologic haz-ards. Seismic risk in Colorado islow to moderate and is not amajor factor in many land-usedecisions. However it needs to beevaluated for certain localitiesand for all critical facilities.According to our statutes, snowavalanching is a geologic hazard,but clear-water flooding is not;both occur in well defined places.Soil settlement and compaction,corrosivity, and erodibility aregeologic hazards as is subsidence,either natural or man-caused.Hazardous-material-contaminationand environmental issues have

4

Figure 1. Map of Colorado showing county boundaries, major physiographic regions, and localities.

Great Plainsand

Rocky MtnPiedmontCentral

Rocky Mtnsand

MontaneBasins

Plateausand

SedimentaryBasins

GrandJunction 2

63

ColoradoSprings

Pueblo

Denver

4

5

1

Plateausand

SedimentaryBasins

CentralRocky Mtns

andMontaneBasins

Great Plainsand

Rocky MtnPiedmont

Numberedlocalitiesare referredto in text

been addressed in our reviews inrecent years as dictated by thegeologic aspects of Federal andState laws and policies. As indi-cated below, interaction(s)between human activities andgeologic conditions or environ-ments, and how they areaddressed in reports havebecome the primary focus ofgeotechnical-investigation evalu-ations made in our reviews.

INVESTIGATIONS OF GEOLOGIC HAZARDS INSUBDIVISIONS AND CGS-REVIEW EXPERIENCESLandslidesThe fundamental issues whichmust be addressed in evaluationof landslides of all types andtheir potential for occurrence insubdivided land are:

1) Have landslides occurred inthe subdivision area in thepast?

2) Are landslides occurringnow and, if so, under whatconditions?

3) Are there materials presentthat could be caused to failas a result of subdividingand developing this land?

During the process of gradingsubdivision land and installingimprovements, earth is moved,drainage is usually changed, andfills are placed. Structural loadscombined with changed ground-moisture conditions resultingfrom septic-system leach fieldsand altered water-runoff patternscan render formerly stable tometastable ground unstable, causing damages ranging fromminor foundation, utility, androad disturbance to completestructural and facility losses.A geotechnical consultant shoulddetermine, after initial fieldexamination of the site, study of

the developer’s plans, and, ifwarranted, materials testing andrisk modeling, the likelihood ofconsequent slope-failure. Basedon data obtained during investi-gations, interpretations can bemade and remedial work can berecommended. In most cases,long-term maintenance plans,especially for slowing or stop-ping active landslides, should beprovided in the geotechnicalreport.

Expansive (Swelling) Soilsand RockFrom our Colorado experiences,occurrences of expansive soilsand rock are nearly always correlative with certain litholo-gies, especially montmorilloniticshales and their derived residu-um, colluvium, and occasionally,alluvium. The expansion poten-tial of weathered, in-placebedrock depends on many factors, according to recent CGSresearch by David C. Noe, of theCGS and others (see “Workingwith Counties...”in this booklet).These factors include the primarycomposition, thickness, andgeometry of different bedrock lay-ers, bedding dip (angle of bed-ding inclination), degree of over-consolidation, thickness ofoverburden soil deposits overbedrock, water table depth, andthe amount of surface water infil-trating the bedrock. Thus, wheremedium- to large-scale geologicmaps or, ideally, maps of expan-sive-soil areas such as those byHart (1974) are available, a con-sultant can usually make a goodfirst approximation of resultingpotential problems for buildingtracts with expansive-soils condi-tions simply by transferring themap data to a larger-scale subdi-vision sketch plan. Where suchmapping is not available, a quick

field check, including inspectionof nearby roads, road cuts, and(damaged) buildings, especiallyin places with drainage prob-lems, often can be helpful.

Following the reconnaissancethe site investigation should bemuch more site-specific. The typ-ical, standardized soils and foun-dation investigation, especiallyfor “lightly loaded residentialstructures” has merit, but toooften consists of a few, too wide-ly spaced and generally loggeddrill holes. The material(s) fromthese dril holes then may be subjected to uniform and simple laboratory tests. These data typi-cally support a “cookbook” commentary about foundationdesign(s) and maintenance. Fewhome builders retain a geotechni-cal engineer to inspect founda-tion excavations and caisson(drilled-shaft or drilled-pier)holes and/or to ensure qualityassurance of foundation con-struction, as is common practicefor commercial and industrialwork. Probably because of cost,most home builders have beenunwilling to invest in more thanan overly simplified soils andfoundation investigation. CGShas noticed a fortunate trendaway from this attitude in thenineties. In the past, standardizedfoundation and other structural-concrete designs, the incentive inthe marketplace to minimize per-square-foot construction costs,the practice of emphasizing housesize over construction quality inreal-estate appraisals, and thenon-existence (in Colorado) ofconcrete-flatwork structural-performance, almost assure fasterhome deterioration and greaterlong-term maintenance and repaircosts for homeowners.

In the opinion of this reportreviewer, the issues above should

5

be better addressed and the like-lihood of the large monetary losses by the public thus could besignificantly reduced. The geo-technical-consulting industryshould make a much strongercase to HUD, real-estate lendersand appraisers, local buildingdepartments, architects, andhome builders for increasing thesophistication and improving thethoroughness of geotechnicalwork. Municipal building depart-ments should be empowered toenforce compliance by homebuilders with recommendationsmade by geotechnical profession-als, especially for relatively moderately priced residentialconstruction. Another aspect ofthe communication problemwhich this consulting industryshould address is public aware-ness of the seriousness and costsof repair of structural damages.To this end, CGS has producedpublications about expansivesoils since 1974; the latest one(Noe and others, 1997) is a main-tenance and landscaping guidefor homebuyers and homeown-ers. About 150,000 copies of itsoriginal (Jochim, 1987) have beensold, mostly to home builderswho are required by Coloradolaw (S.B. 13, 1984) to distributethem at sales closings. The later,updated and expanded versionhad sold about 69,000 copies byend-of-year 1999.

SeismicityColorado has a relatively shorthistory of instrumentally record-ed earthquakes but this is rein-forced by felt earthquake reports,which extends the period ofrecord to about 140 years. Over400 earthquakes have been felt orrecorded in Colorado since 1867.The strongest earthquakes havebeen in the range of magnitude

5.5 to 6.5. In November 1882 anearthquake of magnitude 6.5occurred in Colorado. The epi-center is now believed to havebeen in the mountains of LarimerCounty west of Loveland. It wasfelt throughout Colorado andparts of neighboring states.

Although no complete collapse of structures or deathshave resulted from a Coloradoearthquake, numerous instancesof minor and moderate damagehave occurred. Cracked plaster,cracked walls, cracked and fallenchimneys, broken windows, dishes and other householdgoods, damaged roof tiles, andsimilar effects have been reported for many of Colorado’s earthquakes.

The CGS characterizes theseismic risk as low-moderate.This should not pose a majorproblem for well constructedmodern residential construction,but could pose serious problemsfor older or poorly constructedbuildings, building contents, andinfrastructure.

The seismic hazard is suffi-cient that planning for criticalfacilities, high occupancy build-ings and historic preservation ofold buildings, should considerthe seismic exposure. CGS favorsa building-code approach toplanning and mitigation of this hazard, but this has not yet beenachieved.

Snow AvalanchesSnow avalanches (see “AvalancheFacts” in this booklet) occur frequently during the wintermonths in most of the alpinemountains of Colorado; in fact,Colorado has more areas suscep-tible to them than any other state.Delineation of avalanche startingzones and tracks is a relativelyeasy task based on well defined

parameters as discussed in Mears(1976). Usually, starting zonesand tracks do not present hazards for subdivisions as theyare in places that are so ruggedand steep that they are not devel-opable. However, they can be anextreme hazard to winter-timerecreational users of the backcountry and to persons and vehi-cles on high mountain roadwaysthat traverse them. For subdivi-sions, the hazard-assessmentproblem is usually a determina-tion of frequency of occurrence ofevents of a given magnitude andtype and determination of therunout or “stopping” zone whichis usually on lower valleysideslopes, and, in the case ofmany large events, valley floors.The scientific methods used tostudy snow movement and topredict when, and under whatspecific conditions events of agiven magnitude will occur haveparallels with those for rapidmass movements of earth, e.g.debris flows.

For the geotechnical consul-tant, geologic-hazards assessmentin these areas is a specializedapplied science where compe-tence in engineering and designof “defense” structures, anunderstanding of the rheologyand movement dynamics ofunstable snow pack and movingsnow, and a knowledge of winterweather patterns in the specificarea being studied are absolutelycritical to an adequate investigation.

Water FloodingAlthough not a “geologic hazard” under Colorado law,some kinds of floods, especially“flash” floods in steep mountaindrainages, “cloudburst” floods inarid areas, and those caused byextended rainfall and/or rapid

6

snowmelt, occur coincidentallywith landsliding and rapid ero-sion. Because of this, subdivi-sions that are in these kinds offlood-prone areas, even those inor near small ephemeral drain-ages, almost always need adrainage-control plan. Most ofthese areas are outside of a 100-year floodplain. This plan shouldalways address the effects of thesubdivision on drainage in near-by subdivisions and undevel-oped property that might bedeveloped in the foreseeablefuture.

Soil SettlementSoil settlement is a commonproblem in Colorado where surfi-cial materials are either low den-sity clayey loess, poorly compact-ed eolian sand, soils containingsoluble minerals (e.g., gypsumand halite), or some types of allu-vial (stream-originated)anddebris-flow deposits. These mate-rials occur in many places in Colorado and are the subject of atopical 1997–1998 study by CGS.The loess, which can rangeupward to 30 ft or more in thick-ness, is especially problematicalin higher density, urban, residen-tial subdivisions because, afterhouse construction is completed,residents commonly install land-scaping irrigation. Soon, moder-ate to severe settlement canrapidly occur and pavements aredamaged. Then, owing to its claycontent, the loess may behaveindefinitely as expansive soil. Incases where it is especially thick,it also presents expensive foun-dation-engineering problems as itcan initially settle under struc-tural load. Especially long cais-sons founded in bedrock are fre-quently necessary for successfuldrilled-pier and grade-beamfoundations.

In older subdivisions or inareas heavily irrigated for agri-culture, a perched water table candevelop on relatively imperme-able materials immediatelybeneath sand and in some places,loess. If this contact is above nor-mal foundation depth, anddepending on the expansivity ofthe underlying materials, home-owners can experience problemsranging from extreme structuraldistress to flooded basements.

Commonly these collapsiblesoils are also prone to piping(underground erosion) whichresults in voids that can collapseunpredictability with severe con-sequences for structures built onthem.

With appropriate modifica-tion to geotechnical-investigationtechniques, most of the com-ments applying to consultingpractice in expansive-soil areasalso applies to places with soil-settlement conditions.

Corrosive SoilsCorrosive soils are fairly commonin Colorado and are most com-monly developed on rocks andtheir erosion products that con-tain evaporites. (soluble miner-als). The usual problems arerapid deterioration of conven-tional concrete in contact withsoil and corrosion of buried, baremetal pipes. In the places wherethese soils occur, they were poor-ly understood until relativelyrecently, and older constructionhas thereby been seriously dam-aged if not entirely ruined.

In places where these soilsare likely to occur, CGS expectsthat results of appropriate testingand concrete specifications beincluded in a consultant’s subdi-vision report.

Erodible Soils and RockAlthough all soils and rocks areto some degree erodible, we havemany experiences with two rockunits which have accompaniedmany costly land-developmentproblems in recent years. Thedeeply weathered Pikes PeakGranite of Douglas (Fig. 1, Local-ity 4), Teller (Locality 5), and ElPaso Counties (Colorado Springs)is very erosion-prone. In manyplaces and especially on steeperslopes, it has a thin to absentpedogenic soil. Naturally, its“soil” and grus (a gravel-likeweathering product) support alow-density coniferous forestwith a fragile understory of easi-ly damaged, high altitude grass-es. This granitic terrane was thesource area for the Dawson For-mation which consists predomi-nantly of friable arkosic grit witha poorly developed, clayey, resid-ual soil. The Dawson has a wide-spread outcrop on the RockyMountain piedmont in Douglasand El Paso Counties. The surfi-cial environment and erosioncharacteristics of the Dawson aresimilar to those of the Pikes PeakGranite although in most placesits plant communities are morevaried and slopes on it are lesssteep.

Because of the rapid increasein higher-density subdivisions onthe outcrops of these two forma-tions, what was formerly ranchland and, in privately-ownedmountain areas, summer campsand homes, is now becoming pre-dominantly “bedroom” commu-nities for Denver and ColoradoSprings. Prior to urban develop-ment, cattle grazing and otherpasturing on the piedmont hadseverely damaged the range, andan episode of rapid, ephemeral-stream downcutting (gullying)

7

was well underway. Most of thetrunk-stream beds had becomechoked with granular sedimentwhich greatly changed theirhydrology and riparian habitat.As geologic hazards, these man-accelerated processes have resulted in not only severe dam-age to much of the remainingraw land, but also have increasedmaintenance costs for roads andbridges, increased potential forlandsliding and “muddy”-waterflooding, and caused damages bydeposition of large volumes ofsediment in many residentialsubdivisions.

Addressing and designingmitigation of these adverseeffects on residential subdivisionscan present difficult challengesfor the geotechnical professional.Development plans must be com-bined with very carefullydesigned drainage control forroads and runoff from impervi-ous cover(s). (Re)establishment ofvegetation that will help reducesheet flooding and gullying isdifficult to do and usually justi-fies collaboration with botanistsand landscape architects. Slopeinstability can be greatlyincreased in places adjacent toundercutting streams, and debrisavalanches and flows can be thedirect result of slope denudationduring and after construction.

Ground SubsidenceColorado ground-subsidencehazards are caused by: collapseof abandoned-underground-mineopenings, collapse of solutionvoids in rock units containingevaporites and limestones, andhydrocompaction of soils andsurficial materials caused by dis-solution of soluble minerals.Ground subsidence can, for soils,be considered an extreme case of“soil settlement” as discussed

above. Mining subsidence is byfar the most widespread, and forthat reason, the most serious typesubsidence hazard in Colorado.Localized areas, primarily inEagle and Garfield Counties (Fig.1, Locality 6), have experiencedserious property losses caused bysubsidence and hydrocompactionover the outcrop of the Eagle Val-ley Evaporite. Paleokarst-voidcollapse in Mississippian lime-stones has been reported but hasnot resulted in serious damagesto date.

Colorado’s mining historyextends back to 1859 when placergold was discovered in DouglasCounty. Placer and lode miningof gold and soon thereafter, silvermining, supported many nowfamous mining camps, the majority of which still exist asestablished communities, albeitmost with different economies.Very soon after the inception ofthis mining boom, numerousmountain areas experienced ashortage of wood; what had beenthere was exploited for construc-tion materials, fuel, and minetimbers. This situation, combinedwith railroad development andpresence of exploitable coal,especially on the Front Rangepiedmont and in a few mountainareas, rapidly gave rise to anunderground-coal-mining indus-try, which supplied not only themining camps and railroads, butalso the nearby residential- andcommercial-fuel markets andmany smelters including, eventu-ally, the Colorado Fuel and IronCorporation steel mills at Pueblo.A legacy of all this mining is thatmost of these same areas of theState have mine subsidence andrelated problems. Somewhat iron-ically, far more land was impact-ed by coal mining than metal

mining, the resulting surface haz-ards are usually potentially moresevere over abandoned coalmines, and much of this affectedland is now in populous areas.

It is not possible in this paperto discuss all of the conditionsand parameters that should beaddressed in a mine-subsidence-hazard investigation for landsubdivisions. From our experi-ences the following considera-tions appear to be the most rele-vant:

1) What is the present status ofmine collapse? Has themine collapse gone to com-pletion, and if so, have all ofthe potentially adverse sur-face effects taken place?

2) Was the mining deepenough or is the roof rockand overburden competentenough and is the remain-ing mine void so small that,regardless of the status ofmine collapse, the miningwill never have significantadverse effects on the sur-face (or subdivision)?

3) Is the record (mine map-ping) of mining accurate?How much of a safety (haz-ard) zone should be delin-eated to compensate forpossible inaccuracies inmine mapping? How farbeyond the actual extent ofmining might the surfaceeffects extend, i.e. determi-nation of “angle of draw”.How does mining method,e.g. room-and-pillar versuslong-wall (for coal mining),influence surface-subsi-dence timing and patterns.

4) If applicable, was thereenough subsurface work,e.g. drilling and geophysics,done in the investigation(and provided in the report)

8

and is it interpreted compe-tently and reasonably?

5) Are shafts, adits, anddumps and spoils (especial-ly if they have been regrad-ed and/or used for fills)shown accurately on a mapof the surface. If they havebeen back filled or other-wise “reclaimed”, haveshafts and adits been cor-rectly plugged or sealed offto render their associatedhazards minimal?

6) Are the subsidence-hazard-area delineation(s), surfaceimprovements, and culturalfeatures accurately rectifiedto the subdivision plat?

As for expansive soils, CGShas published a public-informa-tion guide to mine-subsidencehazards (Turney, 1985).

Much of the commentaryabout mine-subsidence investiga-tions also applies to investigationof solution-collapse hazards. Per-haps the most important differ-ences are that there is rarely anyrelevant subsurface mappingavailable and that movement andlocation of ground water, bothbefore and after subdivisiondevelopment, must be considered.We usually recommend that aconsultant map known sinkholesand related features, investigatethe subsurface with drilling andshallow geophysical surveys, anddetermine the hydrologic effectsof the subdivision on naturalground-water conditions.

Hydrocompactive materialsin Colorado are usually rapidlydeposited, low density alluvial-fan and/or sheet-flood depositsderived from rocks containingsoluble minerals. The significantdifference between them and set-tling soils as a geologic hazard isthat the subsidence can be much

greater (upwards to 15 ft inplaces) and can occur rapidly in afew hours. The most commoncause of these movements aredrainage changes which divertwater onto these deposits, espe-cially relocation of irrigationditches by unsuspecting farmersand ranchers. For subdivisionsand roadways, the most advis-able mitigation measure is pre-wetting and compaction followedby regrading.

‘Environmental’ HazardsAlthough they are not includedstrictly in Colorado subdivisionlaws, the kinds of investigationsrequired by the various “environ-mental cleanup” regulations havemade their way into geologic-hazards studies and subdivisionreviews. These two exampleshave been seen often enough Colorado in subdivisions to war-rant comment here:

1) Fills of unknown composi-tion and structural charac-teristics commonly arefound in (re)developingurban and urban-fringeareas, in or near transporta-tion corridors, in miningareas, and on land whichhas been used for many dif-ferent kinds of refuse dumps.One of the most tragic anddifficult to mitigate circum-stances is the widespreadpast use of radioactive ura-nium mill tailings for fill,especially in the GrandJunction area.

2) Leaking underground stor-age tanks (UST’s) and othersources of soil contamina-tion by hazardous materials,including petroleum prod-ucts and agricultural andindustrial chemicals, havebeen located in both urban

and rural subdivisions. Intwo cases we havereviewed, one industrialand one residential, theenvironmental clean-upcosts exceeded the value ofthe undeveloped property.

For the geotechnical profes-sional who is preparing a subdi-vision report for a private client,extreme care should be takenwhen discussing possible envi-ronmental degradation. We haveseen several cases where engi-neering geologists have dis-claimed responsibility for anypart of their investigation thatmight relate to “environmental”matters; others have recommend-ed environmental assessments byspecialist firms. The discussionsby Gerla and Jehn-Dellaport(1989) are probably as relevant toresidential real-estate transfers(i.e.,building-lot sales) as com-mercial ones.

REFERENCESAmuedo and Ivey, Inc., 1975, Coal

mine subsidence and land usein the Boulder-Weld coalfield,Boulder and Weld Counties,Colorado: Colorado Geologi-cal Survey EnvironmentalGeology 9, 92 p., 6 pls.

Costa, J.E. and Bilodeau, S.W.,1982, Geology of Denver, Col-orado, United States of Ameri-ca: Bulletin of the Associationof Engineering Geologists,Vol. XIX, No. 3, p. 261–314.

Gardner, M.E. and Hart, S.S., 1971,Preliminary engineering geo-logic map of the Golden quad-rangle, Jefferson County, Col-orado: U.S. Geological SurveyMap MF-308.

Gerla, P.J. and Jehn-Dellaport, T.,1989, Environmental impactassessment for commercialreal estate transfers: Bulletinof the Association of Engi-

9

neering Geologists, Vol. XXVI,No. 4, p. 531–540.

Hart, S.S., 1974, Potentially swell-ing soil and rock in the FrontRange Urban Corridor, Colo-rado: Colorado GeologicalSurvey Environmental Geol-ogy 10, 23 p., 4 pls.

Jochim, 1987, Home landscapingand maintenance on swellingsoil: Colorado Geological Survey special Publication 14,31 p.

Kirkham, R.L. and Rogers, W.P.,1981, Earthquake potential inColorado: Colorado Geologi-cal Survey Bulletin 43, 175 p.,3 pls.

Mears, A.L., 1976, Guidelines andmethods for detailed snowavalanche hazard investiga-tions in Colorado: ColoradoGeological Bulletin 38, 125 p.

Noe, D.C., Jochim, C.L. and Rogers,W.P., 1997, A guide to swellingsoils for Colorado homebuy-ers and homeowners: Col-orado Geological Survey Spe-cial Publication 43, 76 p.

Robinson and Associates, 1975,Geologic-hazards and land-use planning maps of EagleCounty, Colorado: unpub-lished. (copies on file at theColorado Geological Surveyand Eagle County PlanningDepartment, Eagle)

Rogers, W.P. and Rold, J.W., 1972,Engineering geologic factorsof the Marble Area, GunnisonCounty, Colorado: ColoradoGeological Survey Miscellane-ous Information Series 8, 44 p.

_____, Ladwig, L.R., Hornbaker,A.L., Schwochow, S.D., Hart,S.S., Shelton, D.C., Scroggs,D.L. and Soule, J.M., 1974,Guidelines and criteria foridentification and land-usecontrols in geologic hazardand mineral resource areas:Colorado Geological SurveySpecial Publication 6, 146 p.

Shelton, D.C., 1977, Proceedings,Governor’s third conferenceon environmental geology-geologic factors in land-useplanning, House Bill 1041:Colorado Geological SurveySpecial Publication 8, 111 p.

Soule, J.M., 1976, Geologic hazardsin the Crested Butte-Gunnisonarea, Gunnison County, Col-orado: Colorado GeologicalSurvey Information Series 5,34 p., 9 pls.

_____, 1978, Geologic hazardsstudy in Douglas County, Colorado: Colorado Geologi-cal Survey Open-File Report78-5, 16 pls.

_____, 1980, Engineering geologicmapping and potential geo-logic hazards in Colorado:Bulletin of the InternationalAssociation of EngineeringGeologists, No. 21, p. 121–131.

Turney, J.E., 1985, Subsidenceabove inactive coal mines:information for the home-owner: Colorado GeologicalSurvey Special Publication 26, 32 p.

10

HOW SEVERE IS THEAVALANCHE PROBLEM IN COLORADO?We estimate that 20,000 avalanch-es fall in the Colorado mountainsin an average winter. Most ofthese cause no harm whatsoever.However, since 1980, avalanchesannually cause on average fivedeaths, five severe injuries, morethan $100,000 in direct propertydamage, and more than $1 millionin economic losses. Additionally,avalanches block highways100–200 times per winter.

WHICH COUNTIES HAVEAVALANCHE PROBLEMS? Since 1950, 21 counties have hadat least one avalanche death (seeFigure 1).

WHAT CAN BE DONEABOUT AVALANCHES? Avalanches are forces of natureand cannot be eliminated. How-ever, much can be done to miti-gate avalanche hazards andreduce avalanche accidents. Indeveloped areas, avalanches canbe controlled— either actively byexplosives, or passively by per-manent retaining or divertingstructures. In backcountry areas,forecasting avalanche dangersand educating recreationalistscan reduce accidents.

WHAT IS THE COLORADOAVALANCHE INFORMA-TION CENTER?Founded in 1983, the CAIC is aprogram in the Colorado

Geological Survey. Its mission is to promote safety by reducingthe impact of avalanches onrecreation, industry, and trans-portation in Colorado.

HOW IS THE CAIC FUNDED?The CAIC is entirely cash andfederally funded. Grants anddonations come from the Colora-do Department of Transportation,U.S. Forest Service, local govern-ments including counties andtowns, ski industry, hut and trailassociations, and foundations. In1996–97, revenues were approxi-mately $350,000.

WHAT DOES THE CAIC DO?The CAIC has a staff of 10avalanche experts to carry out aprogram of forecasting, training,and consulting.

ForecastingThe CAIC uses a network of 35observers to provide daily dataon weather, snowpack, andavalanches. We provide thisinformation and a forecast to thepublic via seven hotlines and acomputer bulletinboard. Lastyear there were 126,000 calls tothe hotlines, bulletin board, andhome page for this information.Additionally, 11 mountain radiostations broadcast our hotlinesmessages daily.

TrainingThe CAIC offers avalanche class-es that range from a 2-hour lec-ture to multi-day field courses.

11

AVALANCHE FACTSBY THE COLORADO AVALANCHE INFORMATION CENTER

2812

69

61

4

2412

11

11

51111

5

11

2

1

NORTHERN MTNS

RouttLarimerBoulder

EagleGrand

Clear CreekSummit

CENTRAL MTNS

El PasoGarfield

ParkChaffee

GunnisonLake

Pitkin

SOUTHERN MTNS

ConejosHinsdaleLa PlataMineral

OuraySan Miguel

San Juan

COUNTIES

0 5 10 15 20 25 30

10

Figure 1. Avalanche fatalities in Colorado since 1950.

AVALANCHE FACTSBY THE COLORADO AVALANCHE INFORMATION CENTER

Last year we presented 84 classesto 3,800 people. Additionally, wehave produced two educationalvideos.

ConsultingThe CAIC provides avalancheconsulting services to the skiindustry and CDOT.

WHAT SERVICES CAN THECAIC PROVIDE COLORADOCOUNTIES?The CAIC can provide the fol-lowing services:� Mountain weather forecasts

and backcountry avalanchedanger ratings for use by thepublic and by county roadmaintenance personnel.

� Weather and avalanche fore-casts to sheriffs and search-and-rescue teams during res-cue missions.

� Avalanche education pro-grams and materials.

� Consultation on avoiding,controlling, or otherwisemanaging specific avalancheproblems.

FOR MORE INFORMATIONCONTACTKnox Williams, DirectorColorado Avalanche Information

Center325 Broadway, WS1Boulder, CO 80303-3337(303) 499-9650Fax: (303) 499-9618e-mail: caic@rmi.net

12

AVALANCHE HOTLINESCurrent information on mountain weather, snow, andavalanche conditions are updated daily.

Denver/Boulder (303) 275-5360Colorado Springs (719) 520-0020Fort Collins (970) 482-0457Summit County (970) 668-0600Durango (970) 247-8187Vail (970) 827-5687

METHANE OCCURRENCESGas seeps in the Pine River,ponds, and some water wells inthe Pine River Ranches subdivi-sion (Sec. 14, T. 35 N., R. 7 W.)led La Plata County and Amocopersonnel to test 66 homes nearthe outcrop of the coal-bearingFruitland Formation for methanegas. Sixteen of the tested homeshad detectable levels of methane.

The methane (natural gasbelieved to have emanated fromunderlying coal seams) reachedexplosive levels outside onehouse in the subdivision (AmocoPine River Fruitland OutcropInvestigation, Sept. 15, 1994).Methane seeps were mapped byan Amoco subcontractor in por-tions of a 500 ft wide area in thePine River Valley directly under-lain by the Fruitland Formation.

La Plata County officialsreported that another house neara very active historical gas seepin South Texas Creek (a tributaryof the Pine River) had explosivelevels of probable coal-derivedmethane in the crawl space andunder the kitchen sink (DurangoHerald, Sept. 15, 1994).

Historically active gas seepshave been observed in otherlocalities in the County includingthe Animas River near Durangoand the Soda Springs area nearRed Mesa. Twenty affidavitsattesting to gas seeps which havebeen active for decades are alsoon file with La Plata County Dis-trict Court. Many of these gas

seeps occur where the coal-bear-ing Fruitland or Menefee Forma-tions are exposed (outcrop) ordirectly underlie surface soils orgravels (subcrop).

Approximately one-third ofColorado is underlain by coal(Fig. 1). Much of the coal isdeeply buried, and natural gasgenerated during the coalifica-tion process is trapped in themicropores of the coal at depth.However, coalbed methane gasdoes escape from shallow coalseams and this gas could presenta hazard if trapped in a surfacestructure. This is particularly truein areas where mines were histor-ically gassy.

Gas has been reported inabandoned coal mines in LasAnimas County and was respon-sible for a mine explosion in anactive mine as recently as 1991(Denver Post, Oct. 1, 1994). Gas isbeing vented as part of the min-ing process from operating minesin Rio Blanco, Gunnison, LaPlata, Mesa, and Routt Counties.Coalbed methane is being pro-duced from gas wells in Garfield,La Plata, Rio Blanco, and Las Animas Counties, and has beenproduced to a minor extent inArchuleta and Huerfano Coun-ties.

Although methane gas is colorless, odorless, and non-toxic,it is explosive at 5 to 15 percentmixtures in air. Numerous injur-ies and fatalities in the state’sunderground coal mines havebeen attributed to ignition of

methane released during mining.Methane can also saturate theground and deprive plant rootsof oxygen and the ability toabsorb needed nutrients from thesoil.

Although CGS geologists areunaware of any above-groundlosses of lives or structures dueto coalbed-methane explosions oremissions, the gas occurrences inLa Plata County investigated bythe Pine River Fruitland OutcropInvestigative Team and theincrease in housing developmentand water-well drilling aroundthe state have prompted the CGSto add coalbed methane to ourlist of potential geologic hazards.

The CGS began accumulatingdata about the methane potentialof Colorado coals in 1975 with aU.S. Bureau of Mines grant, andhas continued this research to thepresent. Research objectives areto increase mine safety and pro-ductivity, and to aid in the devel-opment and conservation of thisnew source of pipeline-qualitynatural gas.

In 1978, our earliest coalbedmethane publication reportedmine-gas emissions and explo-sions around the state. Sub-sequent gas-content measure-ments of coal core samples andcoal-basin geologic studiesrevealed that Colorado containedan in-place coalbed methane gasresource in excess of 100 trillioncubic feet. In 1995, 43 percent ofthe natural gas produced in Colo-rado was coalbed methane (Colo-

13

COALBED METHANE—A POTENTIAL GEOLOGIC HAZARD

BY CAROL M. TREMAIN

COALBED METHANE—A POTENTIAL GEOLOGIC HAZARD

BY CAROL M. TREMAIN

rado Oil and Gas ConservationCommission).

Oil and gas seep naturally tothe surface and such seeps led tothe discovery of many of thestate’s oldest oil and gas fields.Where gas is escaping from coals,seeps may be observed in stand-ing or flowing water or in waterwells. Proposed construction sitesdirectly overlying coal seams inthe Raton and Vermejo Forma-tions in the Raton Coal Region,the Fruitland and Menefee For-mations in the San Juan RiverRegion, and the MesaverdeGroup in the Uinta and GreenRiver Regions should be checkedfor visible gas occurrences partic-

ularly where the coal is at or verynear the surface and not coveredby an aquitard.

However, gas seeps may varyseasonally or at much longer cli-matic cycles; a lack of seeps inthe present does not precludetheir occurrence in the future.Long-time rural residents, coalminers, water well drillers, or firesafety personnel may provideadditional information on theoccurrence of methane in an area.Methane concentrations in sus-pect locations can be measuredwith combustible gas detectors oralarms; Amoco has provided anumber of these to concernedresidents in La Plata County. La

Plata County will arrange formethane testing when contactedby residents (La Plata Countymethane health and safetybrochure, 1993).

The CGS recommends thatjurisdictions that have past orongoing coal mining (Fig. 2) con-sult with CGS geologists regard-ing the potential for methaneseeps. For land-use-change pro-posals, such as housing subdivi-sions, methane occurrences mayneed to be addressed as geologichazards as indicated in S.B. 35(1972) and H.B. 1041 (1974). Mea-sures to mitigate and monitormethane-related hazards in exist-ing structures (e.g., ventilation of

14

Figure 1. Coal regions and basins of Colorado.

SEDGWICK

PHILLIPS

YUMA

KIT CARSON

CHEYENNE

KIOWA

PROWERSBENT

BACA

CROWLEY

OTERO

LAS ANIMAS

HUERFANO

PUEBLO

EL PASO

LINCOLN

WASHINGTON

ELBERT

ARAPAHOE

ADAMS

MORGAN

LOGAN

WELD

DOUGLAS

TELLER

LARIMER

BOULDER

JEF

FE

RS

ON

GILPIN

CLEAR CREEK

PARK

CUSTER

FREMONT

SAGUACHE

CHAFFEEGUNNISON

LAKE

SUMMIT

GRAND

JACKSON

COSTILLACONEJOS

ALAMOSARIO GRANDE

MINERAL

HINSDALE

ARCHULETA

EAGLE

ROUTT

PITKIN

LA PLATA

DOLORES

SAN MIGUEL

SANJUAN

OURAY

MONTROSE

DELTA

MESA

GARFIELD

RIO BLANCO

MOFFAT

MONTEZUMA

DENVER

DENVER REGION

SOUTH PARK REGION

CANYON CITY REGION

RATONMESA

REGION

NORTH

PARK

REGION

GREEN RIVER REGION

UINTA

REGION

RIVER REGION

DENVER REGION

SAN JUAN

SAN JUAN BASIN

SAND WASH BASIN

PICEANCE

BASIN

crawl spaces and water wells) doexist. However, prudence dictatessite evaluation for potentialcoalbed-methane hazards prior toconstruction in coal outcrop andsubcrop areas. Published geolog-ic maps and reports on coal andcoalbed methane geology should

provide developers with generalgeologic information on pro-posed development areas. Inareas where coals are near sur-face and historically gassy, adetailed geologic review and pos-sibly soil, structure, or water welltesting may be necessary. Due to

the relatively recent recognitionof this potential hazard, buildingstandards and testing proceduresstill must be formulated in coop-eration with local governmentauthorities.

15

Figure 2. General locations of active and inactive coal mines in Colorado.

SEDGWICK

PHILLIPS

YUMA

KIT CARSON

CHEYENNE

KIOWA

PROWERSBENT

BACA

CROWLEY

OTERO

LAS ANIMAS

HUERFANO

PUEBLO

EL PASOLINCOLN

WASHINGTON

ELBERT

ARAPAHOE

ADAMS

MORGAN

LOGAN

WELD

DOUGLAS

TELLER

LARIMER

BOULDER

JE

FF

ER

SO

N

GILPIN

CLEAR CREEK

PARK

CUSTER

FREMONT

SAGUACHE

CHAFFEE

GUNNISON

LAKE

SUMMIT

GRAND

JACKSON

COSTILLA

CONEJOS

ALAMOSARIO GRANDE

MINERAL

HINSDALE

ARCHULETA

EAGLE

ROUTT

PITKIN

LA PLATA

MONTEZUMA

DOLORES

SAN MIGUEL

SANJUAN

OURAY

MONTROSE

DELTA

MESA

GARFIELD

RIO BLANCO

MOFFAT

DEN

REVIEWSTo review is to make a construc-tive critique and usually meansan assessment of the adequacyand appropriateness of (geo)tech-nical investigations and/or appli-cations of geologic principlesmade by others, mostly profes-sional geotechnical engineers and consulting engineering geolo-gists. CGS reviewers make deci-sions about whether enoughmeaningful work was done, if theresulting report proposes reason-able solutions to problems relat-ed to the geology of the site, andif it offers a technically compe-tent analysis of natural geologicconditions and their potentialimpacts on a proposed activity.

The CGS reviews land-use orland-use-change proposals, asrequired by statute, regulation, orwhen voluntarily requested bypublic or quasi-public entities asfollows:

REVIEW TYPES� Subdivision reviews required

by S.B. 35 (1972) submittedby county planning depart-ments

� Subdivision reviews volun-tarily requested by cities andtowns

� School-site reviews requiredby H.B. 1045 (1984) submittedby School Districts (see adden-dum at the end of this section)

� Water-quality reviews sub-mitted by engineering firmsor other representatives of

water and sanitation districts,local governments, and/orvarious health and sanitationauthorities.

� Miscellaneous reviews of:— landfill proposals— utility alignments— transportation alignments— building-lot construction

suitability— public-facility construction— major development

impacts (e.g., mines, skiareas)

— airport sites and improve-ments

Some counties also requestreviews based on the “matters ofstate interest” provisions of H.B.1041 (1974) which they haveincorporated into their local land-use regulations.

REVIEW PROCESSThe review geologist reads andinterprets submitted reviewmaterials, does backgroundresearch and analysis based onfile and library materials, andmakes a site (field) investigationof the location and/or parcel thatis the subject of the review. Thereviewer then prepares a letterreport to the submitter which discusses the accuracy and ade-quacy of materials prepared byor for the land-use-change propo-nent (e.g., land developer or landsubdivider) and whether addi-tional and/or more technical ordetailed geotechnical workshould be done. The reviewer

offers advice to the submitter andproponent regarding possiblechanges in the proposal whichmight make it more compatiblewith geologic conditions andgeology-related constraints. Inextreme (usually infrequent)cases where an activity mightbecome life or property threaten-ing, the reviewer might recom-mend (rarely) outright denial of aproposal or its major revision. Ifdeemed necessary, the reviewgeologist, planner or other localgovernment official (as appropri-ate), proponent, and the propo-nent’s geotechnical consultantand, sometimes, his attorneymeet or otherwise collaborate toresolve any differences about thegeological feasibility of a propos-al. The ultimate decision aboutacceptance of the final proposalis made by local-government officials, most commonly theBoard of County Commissionersor other local legal, planning, orregulatory authority.

HAZARDS REVIEWEDThe most significant and/orwidespread geologic hazards inColorado, insofar as they threat-en public safety and well beingor cause economic losses, are asfollows. They cannot be rankedby severity unless a specific landuse or human activity in adefined (mapped) susceptiblearea is specified.� Snow avalanches� Landslides (There are many

16

GEOLOGIC HAZARD REVIEWS PERFORMED BYTHE COLORADO GEOLOGICAL SURVEY

BY JAMES M. SOULE

GEOLOGIC HAZARD REVIEWS PERFORMED BYTHE COLORADO GEOLOGICAL SURVEY

BY JAMES M. SOULE

types of such ground move-ments and they are frequentlytransitional to one another.)— rockfalls— mud and debris flows— slumps— rockslides— rock and debris avalanches— earthflows— settlement, subsidence,

and lateral spreading (soilcollapse)

— man-induced ground fail-ure (which may simulateany of the natural typesindicated)

� Seismic (ground-shaking/earthquake) events, bedrockmovements, and their effects

� Ground subsidence causedby underground mining,fluid withdrawal, or rock dissolution

� Nuclear radiation (naturaland man-caused)

� Soil and rock properties(expansivity, chemistry (corrosivity), and bearingcapacity and strength)

� Radioactive and explosivesoil and rock gases (radonand methane)

� Hazardous- and deleterious-material contamination ofrocks, soils, and water

� Soil- and rock-erosion potential

Note: Clear-water (overbank)flooding and fill failures of damsand canal banks are not legallydefined in Colorado as geologichazards. They are not addressedin geologic-hazards reviewsunless they are related to or canbe caused by the geologic hazardsindicated above..

17

INTRODUCTIONThe Colorado Geological Survey(CGS) has reviewed proposalsand plans for all new real-estateacquisitions and facility construc-tion for all Colorado K-12 schooldistricts since enactment of H.B.1045 (1984) (C.R.S. 22-32-124 etseq.). This act provided that the“Board of Education...”, is directedto consult with CGS about“...geologic hazards...” (e.g.,expansive soils, slope instability)“... prior to the acquisition of landfor school building sites or con-struction of any buildings there-on...and to determine the geologicsuitability of the site for its proposed use.” Boards of Educa-tion were also instructed to par-ticipate in local land-use-plan-ning processes and to conformwith construction, fire, and safety codes.

UNDEVELOPED (RAW)LANDThe District is considering aland purchase, trade, or dedication—� School districts usually

acquire land by dedication,trade, or outright purchase.There is a tendency of ownersto offer land which is margin-ally suitable for other devel-opment purposes. Thereviewer assesses the relevant

geologic and geology-relatedconditions for the planneduse of the site.

� School districts can thusavoid involvement with real-estate sales resulting fromacquisition of land whichthey cannot use without sur-mounting serious geology-related development problems.

� Almost all school campusesare a permitted non-conform-ing use in R-1 or R-2 zones.Unless a district plans to usea site in the foreseeable futurefor a school, the reviewerconsiders whether it is moresuitable for residential oropen-space land use.

NEW CONSTRUCTION,RECONSTRUCTION, ANDADDITIONSThe District is going to buildon a new site or modify or addto an existing facility—� Geotechnical and drainage

studies must be relevant toplans and proposed designs.The reviewer evaluates theadequacy of these and indi-cates to district officials andarchitects whether additionalwork is justified.

� A forensic inspection of exist-ing facilities is made to assesstheir condition and to relate

damages or deterioration, if any, to geologic and geolo-gy-related (e.g., soils anddrainage) conditions. Theresulting conclusions areused to support recommen-dations about possible modi-fications of site drainage control, repairs to existingfacilities, and changes in con-struction plans to reduce thepossibility of similar damagesto new construction, rebuild-ing, and additions as applicable.

� Specific siting of new con-struction and its appurte-nances can greatly affect itslong-term servicibility andoverall maintenance andrepair costs. The reviewermay recommend changes insite plans to avoid problemareas and to avoid places thatmay be hazardous to pupils(e.g., drainage and irrigationditches).

EXISTING FACILITIESThe District is ConsideringAcquisition of Developed Property—� All of the appropriate consid-

erations made for undevel-oped land and constructionapply and are considered bythe reviewer.

18

SCHOOL SITE REVIEWS PERFORMED BY THECOLORADO GEOLOGICAL SURVEY

BY JAMES M. SOULE

SCHOOL SITE REVIEWS PERFORMED BY THECOLORADO GEOLOGICAL SURVEY

BY JAMES M. SOULE

1. SMALL SUBDIVISIONREVIEW(Those with lots for ten or fewerdwelling units), also majorreplats of existing approved subdi-visions, rezonings or sketch plansfor twenty acres or less, majoractivity notice reviews, and waterquality application reviews:

Cost = $485.00 prepaid$510.00 not prepaid

2. MEDIUM AND LARGESUBDIVISION REVIEW(Those with lots for more thanten dwelling units), rezoningsor sketch plans for more thantwenty acres:

Cost = $595.00 prepaid$620 not prepaid

Although most reviews listed in 1and 2 above will fall within theestimated time and costs builtinto the listed standard charges,it is necessary, in fairness to allusers, to provide for those casesthat will incur excess reviewcosts. The CGS will contact thelocal planner if it is evident thatadditional review costs will berequested (See discussion in 3below).

3. VERY LARGE OR COM-PLEX SUBDIVISON, GEO-LOGICAL HAZARD REVIEW,MASTER PLAN, OR PUDThese reviews generally requirefield observation and much morereview time. Consequently, costvaries considerably and may

exceed $1,200.00 based uponstandard fee plus additionalreview time and travel cost.

Excess time or travel chargesWill be made for those expendi-tures in excesss of the normalrange of review time (maximum6.75 hours on small reviews or8.75 hours for large reviews), orfor extensive travel related to aparticular case:

Extra review time: at hourlyfee rate of CGS reviewer

Travel at current state rates:Per diem: current state

ratesVehicle mileage :

$0.20/mile; $0.24/mile 4WD

Other travel at actual cost(e.g., auto rental, planefare, etc.).

4. SCHOOL SITE REVIEWSingle school site: $855.00. Multi-ple submittals from the same dis-trict, submitted at the same time:(Not to exceed the number ofsites that can be reasonably visit-ed in one day.) $855.00 for thefirst one, and $700.00 for eachadditional one (includes $155.00reduction for travel.)

5. WRITTEN MINE SUBSI-DENCE HAZARD OPINIONON A RESIDENTIAL LOTFOR REAL ESTATE TRANS-ACTIONThese will be done as quickly aspossible, but five to ten days

lead time is needed in mostcases. $135.00 prepaid, $150.00 otherwise.

As stipulated in C.R.S. 30-28-136, it is the responsibility ofthe county planners, to submitcopies of subdivision plans tothe CGS. It should also be notedthat the statute has beenamended, and now states thatreviewing agencies shall makerecommendations within twenty-one (21) working daysafter the mailing by the county,or its representatives. However,reviews are performed as quickly as possible.

ADDITIONAL SERVICES BY CGS REQUIRING ANAGREEMENT AND PRICEESTIMATEPrice ranges shown here are onlysuggested for general informa-tion. Actual prices will varyaccording to specific needs, sizeand complexity of the individualproject, staff assignment by us,and amount of travel and follow-up work required. Please contactJim Soule (303-866-2611) to dis-cuss details of review or otherproject needs. In come cases, afixed cost may be practical. Inothers, it will be more practical touse hourly fees plus other directcosts attributable to the work.

19

COLORADO GEOLOGICAL SURVEYSTANDARD FEE SCHEDULE FOR

MOST COMMONLY USED SERVICESEFFECTIVE JULY 1, 1994

PH: (303) 866-2611FAX: (303) 866-2461

COLORADO GEOLOGICAL SURVEYSTANDARD FEE SCHEDULE FOR

MOST COMMONLY USED SERVICESEFFECTIVE JULY 1, 1994

TABLE OF SERVICES AND COSTS

Description of Service Estimated Cost or Range Comments

Information regarding other services consistent with our statutory duties on requestAdditions: 1. Fee for bad checks: $25.00

2. Fee for retrieval of archived documents: $25.00 per file3. Invoices for services will be directed to the submitting local government unless another

address is provided.

20

Solid waste disposal application review

Hydrogeological/water quality problems� Septic tank failures� Brine pit contamination� Old landfill� Methane, radon or other contami-

nants in water wells� Hydrocarbon leakage from storage

facilities

Water quality application reviews

Geological review of new local environmen-tal health regulation

Geological hazard studies and reviewsReview of detailed geologic hazard reports:mine subsidence, slope instability, dam siteand/or active fault studies, mudflow/debrisflow mitigation, etc.

Expert testimony in local goverment of otheradministrative or judicial forums

Geological assistance with planning areastudies

Geological hazard or mineral resource con-servation map

Site reconnaissance for facilities (sewagetreatment plants, public buildings, etc.)

Mineral resource and/or conservationreviews Master extraction plan for sand,gravel or quarry aggregate

Specific mineral resource area evaluation

Major quarry aggregate application review,local rezoning, local mining permit, etc.

Small gravel pit or borrow pit application

Basic review, $1500 to $3500,extra for testimony and trav-el, if needed

Standard fee no.1 $485 if pre-paid, otherwise $510

$300 to $700 in most cases

Basic reviews $500 to $3,000plus travel

Minimum approx. $500 forone day, possibly less if mini-mal travel

Highly variable, dependingon time and travel

Highly variable, dependingon size and complexity

Typical $450 to $650, plustravel

Typical cost: $450 to $800

Typical cost: $450 to $800

Typical cost: $1,500 to $3,500

Standard fee no. 1: $485, ifprepaid, $520 otherwise

Basis: 30–40 hours profes-sional time

Highly variable—individual project estimate required

Possible extra charges insome cases

Variable, depending oncomplexity

Recommended individualproject estimate

Cost highly variable,includes preparation time,testimony and travel

Based on actual hours

Recommend individualproject estimate

May be more for largeproject or extensive travel

May be more if issues arecomplex

May be more if issues arecomplex

Depends on size and complexity