reply to exponent responses - final

7/31/2019 Reply to Exponent Responses - Final

1/31

`

Reply to ExponentResponses

Prepared for:

Prepared by:

777 South Figueroa StreetSuite 1100Los Angeles, California 90017

WESTSIDE SUBWAY EXTENSION PROJECTContract No. PS-4350-2000


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3/31

Reply to Exponent ResponsesContents

CONTENTS

1.0 CommentsonExponentResponsetoMetrosApril6Report......................................................... 1

2.0 RelativeRisk:GassyGroundvs.ActiveFaulting.............................................................................. 1

3.0 ManagementofRisksRelatedtoSubsurfaceGasses...................................................................... 2

4.0 MethaneTestingStandards............................................................................................................. 3

5.0

Tunneling

in

Oil

Fields

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

4

6.0 AssessmentofTunnelingSafetyBasedonPastExperience............................................................ 5

7.0 FutureDevelopmentovertheTunnels............................................................................................ 7

8.0 Summary.......................................................................................................................................... 9

9.0 References....................................................................................................................................... 9

Figures

Figure1:BuildingsIndicatedtoBeDemolishedatBHHS............................................................................. 5

Figure2:Figure81fromMetroTunnelingSafetyReport........................................................................... 8

Tables

Table1.ListofSchoolsaboveTransitTunnels............................................................................................. 9

Appendices

Appendix

A

Data

Locations

in

Century

City

AppendixB AdditionalInformationaboutSoilGas

AppendixC FiguresLocationofSchoolsaboveTunnels


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Reply to Exponent ResponsesAcronyms and Abbreviations

ACRONYMS AND ABBREVIATIONS

BHHS BeverlyHillsHighSchool

BHUSD BeverlyHillsUnifiedSchoolDistrict

DTSC DepartmentofToxicSubstancesControl

HDD horizontaldirectionaldrilling

IRP

Metros

Independent

Review

Panel

LADBS LosAngelesDepartmentofBuildingandSafety

OSHA OccupationalSafetyandHealthAdministration

ppbv partsperbillionbyvolume

ppmv partspermillionbyvolume

TAP

(Metro)Tunnel

Advisory

Panel


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Reply to Exponent Responses

1.0Comments on Exponent Response to Metros Apri l 6 Report

1.0 COMMENTS ON EXPONENT RESPONSE TO METROS APRIL 6 REPORTExponentFailureAnalysisInc.(Exponent)hasrespondedonbehalfoftheCityofBeverlyHillstoMetros

April6commentsonExponentsFebruary2012HazardAssessmentStudyReportinitsdocumentdated

April25,2012.ThisreplyreferstothatdocumentasExponentsResponsetoMetroscomments.Metro

isobligatedtoreplytotheApril25document.However,muchoftheExponentresponseissimplyare

statementoftheoriginal(unfounded)assertions.Forsimplificationandclarity,thisreplysummarizes

Exponentsresponsesandreferstopreviousreportswhereapplicable.Thesectionsbelowprovide

ExponentsApril25ResponsesandtheassociatedcommentsbyMetro.

ExponentcontinuestoquestionMetrosevaluationoftheWestsideSubwayalignmentsandtunneling

safetywithrespecttothefollowingconsiderations:

TherelativerisksofthetwoCenturyCityalignmentsrelatedtogassygroundconditionsvs.activefaulting

Theappropriatelevelofinvestigationofsubsurfacegasconditionsandthetestingstandardsthatwereused

Assessmentof

tunneling

safety

based

on

past

experience

and

new

technologyincluding

tunneling

inoilfields

Futuredevelopmentoverthetunnels

2.0 RELATIVE RISK: GASSY GROUND VS. ACTIVE FAULTINGExponentstates:ExponentdisagreeswithMetrosstatedapproachtodealingwithriskandreaffirmsthat

the

acceptable

way

to

assess

and

manage

risk

is

by

performing

the

quantitative

risk

assessment

outlinedinExponentsHazardAssessmentStudy,whichhasbeenusedinmanymajorindustrialand

infrastructureprojects,includingtunnelingprojects.(firstpageExecutiveSummary)

Metroresponse:Exponentcontinuestoproposetheuseofprobabilitybasedriskmanagementanalyses.SomeindividualmembersofMetrosIndependentReviewPanel(IRP)werepersonally

instrumentalintheinitialcreationanddevelopmentoftheconceptofprobabilitybasedrisk

managementandhavebeencontinuouslyinvolvedinitsimplementationforseveraldecades.However,

theIndependentReviewPanel(IRP)believesthattheresultsoftheextensiveanalysisproposedby

Exponentwould

not

be

transparent

and

they

would

be

hard

to

interpret

because

it

would

be

difficult

to

understandwhatfactorsreallycontroltheresults.

TheIRPbelievesthatMetrosapproachtoriskmanagementiscorrect.Aspresentedinitsprevious

responsetoExponent,Metrosapproachtomanagingriskisbyfirsteliminatingfaultrupturerisksthat

areunmanageable.Becauseitisnotpossibletoensurelifesafetyforasubwaystationinanactivefault


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3.0Management of Risks Related to Subsurface Gasses

toSection3.0)thattunnelingorbuildingastationingassysoilscanbeaccomplishedsafelywhenusing

properequipment,

techniques,

and

mitigation

measures.

Moreover,Shannon&Wilson,consultantfortheCityofBeverlyHills,initsreviewoftheCenturyCity

AreaFaultInvestigationReportassertsthatrisksassociatedwithgroundlossduringconstruction,

vibrationsduringconstructionandoperation,andhazardsfrommethaneandothergassescanbe

mitigatedbydesignplansandspecificationsfortheproject.

Theremovalofunmanageableriskanditsreplacementwithmanageableriskthroughprovengas

detectionand

mitigation

technologies

is

the

cornerstone

of

Metros

risk

management

approach.

Metro

reaffirmsthatitsapproachconformstoaccepted,bestpracticesoftheundergroundconstruction

industryandembodiesthesuccessfulriskmanagementproceduresusedonmajorcivilworks,including

transitprojects,throughouttheU.S.andmanypartsoftheworld.

Exponentdoesnotprovideanynewdataonthepresenceofactivefaultingotherthanreferenceto

observationoftrenchesontheBeverlyHillsHighSchool(BHHS)Campus.Metroprovidescommentson

thefaultstudiesbyothersinitsreport,ResponsetoLeightonConsultingReport,May14,2012.In

additiontothatreport,Metrohasmadepreviousstatementsabouttheapplicabilityoftrench

investigationsandtheabsenceoffaultingattheConstellationStationsite.RefertoMetrosResponseto

Shannon&Wilson,April17,2012,fordiscussionoftrenches.

3.0 MANAGEMENT OF RISKS RELATED TO SUBSURFACE GASSESExponentmaintainsthatrisksassociatedwithsoilgasmaybecomparableto,orgreaterthan,thoseassociatedwithactivefaulting.Metrodisagrees.Asdiscussedabove,activefaultingalongSantaMonicaBoulevardisasourceofunmanageableriskthatmustbeavoided.Incontrast,soilgasriskscanbe

mitigatedsafely

and

are

done

so

on

aroutine

basis.

Modern

soil

gas

mitigation

measures

for

subter

raneanstructuresarewellestablishedandhaveproventobehighlyeffective.Severalexcavationsfor

subterraneanparking,someevendeeperthantheproposedCenturyCityConstellationStation,have

beenconstructedandoperatedsafelyintheimmediatevicinityoftheproposedstation.Metrohas

compileddataontheseprojectsinconjunctionwithitsalignmentassessmentactivities.Thedatashow

thatpreviousrudimentarygasmitigationmeasureshavebeeneffective.Moreover,gasmitigation

technologyhasimprovedsubstantiallyinrecentyears.Themoderngasmitigationtechnology,whichwill

beincorporatedintotheConstellationStation,operateswithadditionallevelsofredundancythat

reducethe

risk

of

gas

intrusion

to

insignificant

levels.

Exponent

apparently

agrees,

as

it

states,

Exponentdidnotcontendthattunnelingorbuildingastationingassysoilscouldnotbe

accomplishedsafely(page9).

Exponent(pages9and10)expressedconcernaboutthesufficiencyofsoilgasdatawestofBHHSnear

the proposed Constellation Station. It should be recognized that many gas probes have been installed


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4.0Methane Testing Standards

CenturyCityFaultInvestigationReportshowsthelocationsofmorethan100boringsinthevicinityof

theproposed

Constellation

Station.

This

figure

illustrates

the

vast

amount

of

relevant

subsurface

data

thathasbeencollectedandreviewedwithrespecttotheConstellationStation.

FromallthedatacollectedandreviewedintheCenturyCity/BeverlyHillsareatodate,Metrois

confidentthatthegaslevelsatBHHSarelowerthanthosefoundinsomeotherareasofthecitywhere

safeandsuccessfultunnelinghasbeenperformed.Inover20yearstherehavebeennosafetyrelated

problemswithgasduringMetrotunnelingandsubsequenttunneloperations.

Metro

has

requested

access

to

the

BHHS

site

for

independent

installation

of

soil

gas

probes.

Beverly

Hills

UnifiedSchoolDistrict(BHUSD)hasnotyetagreedtoallowMetrotoproceedwiththeproposed

additionalinstallations.Accordingly,thesemeasurementswillbedoneduringfinaldesigntodetermine

whatprotectivemeasuresormonitoringarerequiredtoensurethesafetyofstudents.Gas

concentrationsalonedonotconfirmthatahazardexistsatasite.Otherfactors,suchaspressuresand

potentialflowvolumes,areevenmoreimportant.Nevertheless,thegasconcentrationsreportedinthe

vicinityofBHHSarelowerthanconcentrationsfoundinotherareasofthecitythathavebeen

successfullytunneledbyMetroorexcavatedbyMetroforstationsandotherundergroundfacilities.

Asafurthernote,Metroisawareofmuchmisinformationaboutsoilgasisbeingdisseminated.

AppendixBpresentsadditionalinformationaboutsoilgasandconstructingingassyground.

4.0 METHANE TESTING STANDARDSExponentstates(regardingtestingstandardsforsubsurfacegases):.TheMetroreports(includinginformationcontainedinAppendixLoftheMetroFinalEIS/EIR)donotpresentspecificjustification(in

theformofastandardorguideline)fortheselectionofthelocationsorspacingbetweenthegas

monitoringwells

or

borings.

It

appears

that

no

gas

investigation

standards

were

followed

as

none

werereferencedinMetrosTunnelingSafetyReport.

Metroresponse:Basedupontheaboveassumption,Exponentfurthersuggeststhathighqualitysoilgasdatadoesnotexistfortheproject.Exponentreferencesthreepublicationsthatcontainsoilgastesting

guidelinesthatitassertswerenotfollowed.ItshouldbenotedthatMetrossoilgasconsultantswere

involvedwiththedevelopmentofallthreeofthereferencedguidelines.Eachoftheguidelinesisnot

applicabletotheWestsideSubwayproject.ThetestingguidelinescitedbyExponentweredevelopedfor

specifictypes

of

projects,

such

as

for

the

assessment

of

new

buildings

on

grade

or

with

basements.

The

guidelineswerenotdevelopedforapplicationtotunnelingprojects.

Forexample,Exponentreferenceda100footgridtestingprotocolformethaneinvestigationsatschool

sitesthatisforidentificationofpotentialmethanesourceareassuchassettlingpondsandmanurepile

areas,andisnotappropriatetoassessgasforatunnelingproject.


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5.0Tunneling in Oil Fields

ProjectaremorerigorousanddetailedthantheproceduresreferencedbyExponent.Theamount,

diversity,duration,

redundancy,

and

quality

of

the

soil

gas

data

that

have

been

compiled

for

the

WestsideSubwayExtensionProjectmeet,orexceed,theobjectivesthataresetforthinthereferences

citedbyExponentandaresufficientfortunnelalignmentselection.Moreover,additionalsoilgastesting

willbeconductedduringfinaldesign.Accordingly,thereisnobasisforExponentssuggestionthat

appropriateguidelineswerenotfollowedorthathighqualitydatawasnotcollected.

5.0 TUNNELING IN OIL FIELDSExponentstates:TheMetroResponseReportmentionsthathorizontaldirectionaldrilling(HDD)willtakeplaceforexplorationbeneathBHHSbuildingsduringthenextphasesofdesign(i.e.afterthetunnelalignmenthasalreadybeenselected).ItisExponentsopinionthattheHDDshouldoccurduring

thepreliminarydesignphaseinordertoconsiderallrisksassociatedwithaparticularalignment

option.(Section6,Page11)

Metroresponse:ExponentagreeswithMetrosplantousehorizontaldirectionaldrilling(HDD)toprobeusingmagnetometerstolocateanyabandonedoilwellcasingsalongthetunnelalignmentpriorto

tunneling.

Metro

has

investigated

the

methods

and

plans

to

proceed

with

HDD

during

final

design.

If

a

wellcasingislocated,therewouldbesufficienttimetoremoveitordependingonthewelllocation

adjustthealignmentslightlytoavoidit beforethetunnelboringmachinereachesthearea.

Exponentstates:ExponentexpressesconcernforpotentialgroundsettlementsandimpactsontheBHHSbuildingiftheTBMisstoppedbeneaththebuildinginordertoabandonanoilwellcasing.

Metroresponse:ShouldanoilwellcasingbefoundtobelocatedalongthealignmentandbeneathacurrentBHHSbuilding,severalalternativeswillbeconsidered.Thesituationlendsitselftofull

cooperationbetween

Metro

and

BHUSD

for

an

opportunity

to

explore

the

site

conditions

for

the

purposeofmutuallyoptimizingtheinteractionoftunnelingandfuturedevelopmentofthehighschool.

BHHSplansforfuturedevelopment(ModernizationPlan2009,Figure1)showthattheportionofthe

buildingbeneathwhichthetunnelwouldbeadvancedwouldberemoved.Inthiscase,accessforwell

abandonmentandcasingremovalwouldbegainedfromthesurfacepriortotunneling.Iftheexisting

buildingweretoremaininplace,shouldawellcasingbedetected,considerationwouldbegivento

eitheradjustingalignmentslightlytoavoidacasingortogainingaccessusinggroundcontrol

procedures,suchasgroutingorfreezing,toexcavateandremovethecasingpriortotunnelingwithout

impactingthe

buildings

above.

It

is

emphasized

that

the

probability

of

encountering

an

oil

well

on

the

tunnelalignmentanddirectlyundertheschoolbuildingsisverylow.Thereisnoevidencefromavailable

DivisionofOil,Gas,andGeothermalResourcesrecordsorfromhistoricphotosoftheexistenceofoil

wellsundertheBHHSbuildingsalongtheproposedalignment.


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6.0Assessment of Tunneling Safety Based on Past Experience

Figure 1: Buildings Indicated to Be Demolished at BHHS

6.0 ASSESSMENT OF TUNNELING SAFETY BASED ON PAST EXPERIENCEExponentstates(withrespecttoSection5oftheirHazardAssessmentStudy):Thepurposeofdiscussingpastprojectswasnottodrawcomparisonsbetweendifferenttunnelingmethods,butto

showwhatcanoccurwhenproperproceduresarenotfollowedorwhenunexpectedgroundconditions

orworkstoppagesareencountered.

Metroresponse:AsMetronotedinitsApril11response,Exponentreferencedpasttunnelsdrivenwithopenfaceshields.OpenfaceshieldsarenolongerusedonMetroprojects.Potentialissuesrelatedto

theirusearenotrelevanttopressurizedfaceshieldsthatarenowrequiredonMetroprojects.Itisagain

emphasizedthattheproperprocedureistorequiretheuseofthepressurizedfaceshieldsandprovide

criteriaandmonitorperformancetoensurethatrequirementsaremet.


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6.0Assessment of Tunneling Safety Based on Past Experience

throughouttheentire1.7milelengthofeachofthetwoEPBtunnelsdrivenonMetrosMGLEEprojectin

2006.The

result

was

achieved

with

normal

operation

of

the

TBM,

which

includes

control

of

machine

performanceandmonitoringtoconfirmthatgroundmovementsarebeingcontrolledtorequiredlevels.

Further,asnotedinMetrospreviousresponse,groundlossoflessthan0.5percentisnowroutineon

pressurefacetunnelingprojectsrecentexamplesincludeCityofPortlandEastandWestsideCSO

tunnelsandtheUniversityLinktransittunnelsinSeattle,wheremostofthefourtunneldriveswere

beneathbuildings.AprimeinternationalexampleistheexperienceonLine9oftheBarcelonaMetro.

Theachievementwasparticularlyimpressivebecauseitwaswithlargediametershields(31and39feet

diameter)driven

over

most

of

the

alignment,

beneath

buildings.

Bono,

et

al

(2008),

with

the

contractor

Paymacotas,state:

According to our experience inBarcelona, even in very different geological contests

(sic) rangingfrom Pliocene clay/sands to Olocenic low consolidated silts with covers

rangingfrom 1.5to 2 diameters, it is currentlypossible to reach a negligible surface

settlement,maintainingtheapparentvolumelosseswellbelowthe0.5%.

Thishasbeenpossiblewiththeimplementationofadetailedgroundmonitoringwhich

is continuously feeding a back analysis process to set the EPB shield excavation

parametersjointlywithastrictcontrolcarriedoutdirectlyintheEPBshield.

WithrespecttoBHHS,Shannon&Wilson,consultantfortheCityofBeverlyHills,initsreviewofthe

CenturyCityAreaFaultInvestigationReport,assertsthatthetunnelisnotlikelytodirectlyimpactthe

campusfacilities.Theyfurtherindicatethattherisksassociatedwithgroundlossduringconstruction,

vibrationsduringconstructionandoperation,andhazardsfrommethaneandothergassescanbe

mitigatedbydesignplansandspecificationsfortheproject.

Exponentstates:theabsenceofpastincidentsdoesnot,byitself,ensurethatfuturetunnelingin

similarconditionsisinherentlysafe.

Metroresponse:Theabovestatementiscorrectiftherequirementsandconditionsnecessarytoachievethepreviousgoodperformancearenotunderstoodandproperlyappliedonthefutureproject.

However,thisisnotthecase.Groundcontrolrequirementsarewellunderstoodandarebeingapplied

forthecurrentandfutureMetrotunnelprojects.

Exponentstates:Furthermore,tunnelalignmentcomparisonsandnecessaryprecautionscannotbemadewithoutincorporatingpossibleoutcomesofexcessivesettlementintoanoverallframeworkfor

quantitativeriskassessment.

Metroresponse:Metrodisagrees.Ratherthanconductingaquantitativeriskassessmentofthet f i ttl t th ti l d b M t t it


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7.0Future Development over the Tunnels

Contractorworkplansubmittalsforcontrollingoperation,includingtargetandwarninglevelsforkey

machine

functions

MonitoringofgroundmovementsaroundshieldandfeedbacktomachineoperationExponentstates:However,therisksalwaysexistforunexpectedconditions.Severalsourcesofgrounddisplacement,specifictopressurized,closedfaceTBMs,includethefollowing(Boone,2008).

Metroresponse:TheBoonereferenceoutlinessourcesofgroundmovementaroundtheface,body,andtailoftheshield.Manyareconditionsthatarenotunexpectedrisksbutaredealtwithinthedesignand

operationof

the

shield.

Metros

consultants

have

evaluated

and

summarized

sources

of

ground

loss,

includingthoseoutlinedintheBoonereference,basedontheirownpioneeringfieldinvestigationswith

openshieldsaswellasrecentinvestigationsofpressurefaceshieldsthathavedemonstratedtheir

capabilitytolimitgroundmovementsaroundthefaceandperimeteroftheshield.Mostimportantly,

provenproceduresforcontrollingtheseconditionshavebeenidentifiedandapplied.

7.0 FUTURE DEVELOPMENT OVER THE TUNNELSExponentstates:Onpage71oftheirResponseReport,Metrostatesthatspecialfoundationswouldnotberequiredforstructuresplacedabovethetunnels.However,thiswouldbetrueonlyforfuture

structuresthatlieaboveoroutsideofMetrosRightofWayEnvelope.Thepreliminarytunnelprofiles

underBHHSshowthetunnelcrowntobeapproximately55to70feetbelowgrade,leavingapproxi

mately30to50feetofclearanceforundergroundstructuresandfoundations.Thisamountof

clearancemaybesufficientfortwotofourlevelsofundergroundparkingonamatfoundation.

However,othertypesofstructuresmayrequiredifferentfoundationsthatconsistofpilesordrilled

piersthatextendintoMetrosRightofWayEnvelope.IntheResponseReport,MetrostatesthatAny

futureproject

to

be

developed

adjacent

to

Metro

right of

way

will

need

Metro

approval

prior

to

construction.CloserguidanceandexpectationsshouldbeprovidedbyMetroaboutanyconstruction

approvalprocessesrequiredbythem.

Metroresponse:ThistopicwascoveredinMetrosTunnelingSafetyreport(Section8.0),butitappearsthattherearemisconceptionsregardingMetrosRightofWayEnvelopeandrequirementsforlocating

structuresaboveandadjacenttoMetrotunnels.Guidanceontheconstructionapprovalprocesscanbe

foundinMetrosAdjacentConstructionDesignManual(R9DE3033.00).Reviewofproposeddesigns

thatcould

have

adirect

impact

on

aMetro

facility

or

structure

is

required,

but

specific

requirements

for

offsetsandstandoffdistancesfromthetunnelsarenotgivenbecauseeachprojectanditsrelation

shiptotheMetrofacilityisuniqueandsolutionsneedtobemadeonacasebycasebasis.Metrolooks

forwardtotheopportunitytoworkwithBHHStodevelopacceptablesolutionsforproposed

foundationsorundergroundfacilitiesinthevicinityofthetunnels.

M t R il Ci il D i C it i d fi i ht f li it f th t l f l t t i iti


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7.0Future Development over the Tunnels

Nearsurfacestructureswithshallowfoundationsandbasementscanbeconstructedabovethetunnels.

Clearances

above

the

proposed

tunnel

crown

are

sufficient

for

multiple

levels

of

undergroundparking.

Constructionofbasementsorundergroundparkingstructuresonmatfoundationsreducestheloadonunderlyingstructures,makingitfeasibletoplacethefoundationmatincloseproximitytothe

crownoftheunderlyingtunnel.Theweightofthesoilremovedisusuallymorethantheweightof

thestructure.

Deepfoundations,suchasdrilledpiers,canbeplacedadjacentto,andbetween,thetunnels.Figure 2: Figure 8-1 from Metro Tunneling Safety Report


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8.0Summary

Asanadditionalnote,Metroresearchedwheretunnelshavebeensafelyconstructedunderschoolsor

whereschools

have

been

constructed

above

tunnels.

A

few

examples

in

North

America

are

listed

in

Table1.

Table 1. List o f Schools above Transit Tunnels

Name of School Location Building DateDate TunnelConstructed

Camino Nuevo Charter Academy Los Angeles, CA ~ 1994 1993

The Northwest School Seattle, WA 1905 2012Bentley School Oakland, CA ~1928 1970s

East Sylvan Middle School Portland, OR Prior to tunnel 1990's

West Portal Elementary School San Francisco, CA 1927 1918

Rooftop Elementary School San Francisco, CA 1953 1918

8.0 SUMMARYMetroreconfirmstheconclusionsprovidedinthetwoCenturyCityInvestigationreportsandinits

TunnelAdvisoryPanel(TAP)ReportissuedonOctober19,2011:

MetrosapproachtoRiskManagementiscorrect. Becauseofknownactivefaulting,stationsitesalongSantaMonicaBoulevardareunacceptablefora

subwaystation.FurtherdiscussionoffaultingisprovidedinMetrosresponsestoLeighton

ConsultingandShannonandWilson.

ThereisnoactivefaultingattheConstellationStationsiteandthelocationissuitableforastation. TunnelingcanbesafelyaccomplishedalongtheConstellationalignmentandunderBHHSand

adjacentproperties.Thisincludesconstructioningassygroundandoilproducingareas.

ThepresenceofthetunnelswillnotprecludeexpansionanddevelopmentoftheHighschool.

9.0 REFERENCESBonoet.al.,2008,SurfaceSettlementMinimizationinSoftSoilwhenExcavatingwithandEarth

PressureBalanceShield,(PaperinEnglish), JournadaTechnical:TunelesConEPB:SimulatcionyControl

delaTuneladora,UniveritatPolitecnicadeCatalunyaUniversidad

LosAngelesCountyMetropolitanTransportationAuthority.AdjacentConstructionDesignManual(R9

DE303 3 00)


14/31


9.0References

LosAngelesCountyMetropolitanTransportationAuthority.May2012.WestsideSubwayExtension

ProjectResponse

to

Leighton

Consulting

Report

(DRAFT).

LosAngelesCountyMetropolitanTransportationAuthority.April4,2012.WestsideSubwayExtension

ProjectResponsetoHazardAssessmentStudybyExponent.

LosAngelesCountyMetropolitanTransportationAuthority.April17,2012.WestsideSubwayExtension

ProjectResponsetoPreliminaryReviewcommentsofCenturyCityAreaFaultInvestigationReportby

Shannon&Wilson.


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Reply to Exponent ResponsesAppendix AData Locations in Century City

APPENDIX A DATA LOCATIONS INCENTURY CITY


16/31


17/31

Reply to Exponent ResponsesAppendix AData Locations in Century City

W E S T S I D E S U B W A Y E X T E N S I O N P R O J E C T

May 15, 2012 Page A-1

APPENDIX A DATA LOCATIONS IN CENTURY CITY

Plate 2 From Century City Tunneling Safety Report


18/31


19/31

Reply to Exponent ResponsesAppendix BAdditional Information about Soil Gas

APPENDIX B ADDITIONAL INFORMATIONABOUT SOIL GAS


20/31


21/31

Reply to Exponent ResponsesAppendix BAdditional Information about Soil Gas

APPENDIX B ADDITIONAL INFORMATION ABOUT SOIL GAS

ItisclearthatmanypeoplehavesincereconcernregardinggassafetyatBeverlyHillsHighSchool.

Itisimportanttoknowthatanextensivebodyofinformationisavailableregardingthecontrolof

methanesoilgasandhydrogensulfide,includingregulatoryguidelinesandthehistoricalexperienceat

manyprojectsitesinSouthernCaliforniaandindeedaroundthenation.Theseguidelineshavebeen

successfullyemployedformanyyears.Baseduponthisknowledgeandguidance,decisionscanbemade

confidently.ItshouldbenotedthateventhehighprofilesoilgassitesinLosAngelesoverthelast

severaldecades

have

been

successfully

mitigated

and

are

currently

occupied.

Itisimportanttounderstandthatthegashazardorriskduringtunnelingisrelatedtothevolume,

concentration,andpressureofthegasinthesurroundingsoil.Gasconcentrationsarenotthesamein

thetunnelastheyareinthesoilbecausethesoilpermeabilityandthepresenceofthetunnellining

limitstheflowofgasintothetunnelandbecauseventilationisprovidedtodiluteandremovegasesthat

enterthetunnel.

Experience

in

Los

Angeles,

and

in

other

cities

in

the

United

States

and

world

wide,

has

shown

that

the

propercombinationofdesign,moderntunnelingequipmentandmethods,andasupplyofsufficient

ventilationleadtosuccessfultunnelconstructionandoperationsingassyground.


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23/31

Reply to Exponent ResponsesAppendix CFigures Location of Schools above Tunnels

APPENDIX C FIGURES LOCATION OFSCHOOLS ABOVE TUNNELS


24/31


25/31

7thStreet

Camino NuevoCharter Academy

Esperanza PublicElementary School

Macarthur Park Station

Metro Subway Tunnels


26/31


27/31

The Northwest School


28/31


29/31

West Portal PublicElementary School


30/31


31/31

Rooftop K-8 PublicAlternative School

reply to exponent responses - final

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