<SEC-DOCUMENT>0000831641-21-000096.txt : 20211122
<SEC-HEADER>0000831641-21-000096.hdr.sgml : 20211122
<ACCEPTANCE-DATETIME>20211122194126
ACCESSION NUMBER:		0000831641-21-000096
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20211118
FILED AS OF DATE:		20211122
DATE AS OF CHANGE:		20211122

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			CHRISTENSEN CRAIG L
		CENTRAL INDEX KEY:			0001206709

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-19655
		FILM NUMBER:		211434256

	MAIL ADDRESS:	
		STREET 1:		3475 EAST FOOTHILL BOULEVARD
		CITY:			PASADENA
		STATE:			CA
		ZIP:			91107

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			TETRA TECH INC
		CENTRAL INDEX KEY:			0000831641
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-ENGINEERING SERVICES [8711]
		IRS NUMBER:				954148514
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1003

	BUSINESS ADDRESS:	
		STREET 1:		3475 EAST FOOTHILL BOULEVARD
		CITY:			PASADENA
		STATE:			CA
		ZIP:			91107
		BUSINESS PHONE:		6263514664

	MAIL ADDRESS:	
		STREET 1:		3475 EAST FOOTHILL BOULEVARD
		CITY:			PASADENA
		STATE:			CA
		ZIP:			91107
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
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<DESCRIPTION>FORM 4
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        <issuerName>TETRA TECH INC</issuerName>
        <issuerTradingSymbol>TTEK</issuerTradingSymbol>
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            <rptOwnerName>CHRISTENSEN CRAIG L</rptOwnerName>
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            <rptOwnerStreet2></rptOwnerStreet2>
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            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>91107</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
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            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>SVP, CIO</officerTitle>
            <otherText></otherText>
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    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>RESTRICTED STOCK UNITS (RIGHT TO RECEIVE)</value>
            </securityTitle>
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                <transactionPricePerShare>
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                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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            </transactionAmounts>
            <exerciseDate>
                <value>2019-11-18</value>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <value>2022-11-18</value>
            </expirationDate>
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                <underlyingSecurityTitle>
                    <value>COMMON STOCK</value>
                </underlyingSecurityTitle>
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                    <value>D</value>
                </transactionAcquiredDisposedCode>
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                <value>2021-11-18</value>
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                <value>2024-11-19</value>
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                    <value>922</value>
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    <footnotes>
        <footnote id="F1">The award becomes vested as to 25% of the RSUs on the anniversary of the grant date.</footnote>
        <footnote id="F2">Represents the combined number of shares withheld to pay the related tax liability on a total of 1,684 restricted stock units (RSUs) which vested on 11/18/2021.</footnote>
        <footnote id="F3">The RSUs become vested as to 25% of the shares on November 18, 2019, and the anniversary of that date going forward until fully vested.</footnote>
        <footnote id="F4">The RSUs become vested as to 25% of the shares on November 18, 2020, and the anniversary of that date going forward until fully vested.</footnote>
        <footnote id="F5">The RSUs become vested as to 25% of the shares on November 18, 2021, and the anniversary of that date going forward until fully vested.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Preston Hopson, Attorney-in-fact for Craig L. Christensen</signatureName>
        <signatureDate>2021-11-23</signatureDate>
    </ownerSignature>
</ownershipDocument>
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</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
