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  <xs:element id="ttek_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseLegalContingencyChargeAmount" abstract="false" name="EffectiveIncomeTaxRateReconciliationNondeductibleExpenseLegalContingencyChargeAmount" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ttek_EffectiveIncomeTaxRateReconciliationExcludingValuationAllowanceReleaseNonDeductibleGoodwillImpairmentTransactionCostsAndExcessTaxBenefitsOnShareBasedPaymentsPercent" abstract="false" name="EffectiveIncomeTaxRateReconciliationExcludingValuationAllowanceReleaseNonDeductibleGoodwillImpairmentTransactionCostsAndExcessTaxBenefitsOnShareBasedPaymentsPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ttek_LiabilityForUncertainTaxPositionsCurrentAndNoncurrent" abstract="false" name="LiabilityForUncertainTaxPositionsCurrentAndNoncurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ttek_OperatingSegmentsExcludingIntersegmentEliminationMember" abstract="true" name="OperatingSegmentsExcludingIntersegmentEliminationMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ttek_A2028SeniorNotesMember" abstract="true" name="A2028SeniorNotesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ttek_TermLoanFacilityDue2027Member" abstract="true" name="TermLoanFacilityDue2027Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ttek_TermLoanFacilityDue2026Member" abstract="true" name="TermLoanFacilityDue2026Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ttek_SecondAmendedCreditAgreementMember" abstract="true" name="SecondAmendedCreditAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ttek_ThirdAmendedCreditAgreementMember" abstract="true" name="ThirdAmendedCreditAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ttek_FourthAmendedRestatedCreditAgreementMember" abstract="true" name="FourthAmendedRestatedCreditAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ttek_AmendedCreditAgreementMember" abstract="true" name="AmendedCreditAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ttek_OtherCreditFacilitiesMember" abstract="true" name="OtherCreditFacilitiesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ttek_TermLoanFacilityMember" abstract="true" name="TermLoanFacilityMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ttek_A3YTermLoanFacilityMember" abstract="true" name="A3YTermLoanFacilityMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ttek_A5YTermLoanFacilityMember" abstract="true" name="A5YTermLoanFacilityMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ttek_AmendedRevolvingCreditFacilityMember" abstract="true" name="AmendedRevolvingCreditFacilityMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ttek_LineOfCreditMulticurrencyBorrowingsAndLettersOfCreditMember" abstract="true" name="LineOfCreditMulticurrencyBorrowingsAndLettersOfCreditMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ttek_VariableRateComponentAxis" abstract="true" name="VariableRateComponentAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="ttek_VariableRateComponentDomain" abstract="true" name="VariableRateComponentDomain" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ttek_PaymentsForCappedCalls" abstract="false" name="PaymentsForCappedCalls" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ttek_DerivativeCapPricePerShare" abstract="false" name="DerivativeCapPricePerShare" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="ttek_CapPricePremiumOverReportedSalesPricePercentage" abstract="false" name="CapPricePremiumOverReportedSalesPricePercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="ttek_CommonStockReportedSalesPrice" abstract="false" name="CommonStockReportedSalesPrice" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="ttek_LineOfCreditFacilityAccordionFeatureHigherBorrowingCapacityOption" abstract="false" name="LineOfCreditFacilityAccordionFeatureHigherBorrowingCapacityOption" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ttek_LineOfCreditFacilityAccordionFeatureIncreaseLimit" abstract="false" name="LineOfCreditFacilityAccordionFeatureIncreaseLimit" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ttek_LineOfCreditAmortizationOfPrincipalAmountYearOnePercent" abstract="false" name="LineOfCreditAmortizationOfPrincipalAmountYearOnePercent" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ttek_LineOfCreditAmortizationOfPrincipalAmountYearTwoPercent" abstract="false" name="LineOfCreditAmortizationOfPrincipalAmountYearTwoPercent" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ttek_LineOfCreditAmortizationOfPrincipalAmountYearThreePercent" abstract="false" name="LineOfCreditAmortizationOfPrincipalAmountYearThreePercent" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ttek_LineOfCreditAmortizationOfPrincipalAmountYearFourPercent" abstract="false" name="LineOfCreditAmortizationOfPrincipalAmountYearFourPercent" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ttek_LineOfCreditAmortizationOfPrincipalAmountYearFivePercent" abstract="false" name="LineOfCreditAmortizationOfPrincipalAmountYearFivePercent" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ttek_LineOfCreditFacilityCovenantConsolidatedLeverageRatioMaximum" abstract="false" name="LineOfCreditFacilityCovenantConsolidatedLeverageRatioMaximum" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="ttek_LineOfCreditFacilityCovenantConsolidatedInterestCoverageRatioMinimum" abstract="false" name="LineOfCreditFacilityCovenantConsolidatedInterestCoverageRatioMinimum" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="ttek_RatioOfConsolidatedFixedChargeCoverageRatio" abstract="false" name="RatioOfConsolidatedFixedChargeCoverageRatio" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="ttek_FCAClaimsMember" abstract="true" name="FCAClaimsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ttek_CERCLAClaimsMember" abstract="true" name="CERCLAClaimsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ttek_LossContingencyNumberOfActions" abstract="false" name="LossContingencyNumberOfActions" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="ttek_LegalFeesAncillaryClaims" abstract="false" name="LegalFeesAncillaryClaims" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
</xs:schema>
