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( Mark One ) ■ UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Fiscal Year Ended October 3 , 2021 TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Transition Period from FORM 10 - K Commission File Number 0-19655 TETRA TECH , INC . ( Exact name of registrant as specified in its charter ) Delaware ( State or other jurisdiction of incorporation or organization ) Securities registered pursuant to Section 12 ( b ) of the Act : Title of each class Common Stock , $ 0.01 par value 3475 East Foothill Boulevard , Pasadena , California 91107 ( Address of principal executive offices ) ( Zip Code ) ( 626 ) 351-4664 ( Registrant's telephone number , including area code ) Trading Symbol ( s ) TTEK ( I.R.S. Employer Identification No. ) to Securities registered pursuant to Section 12 ( g ) of the Act : None 95-4148514 Name of each exchange on which registered The NASDAQ Stock Market LLC Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Yes > No Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Act . Yes No Indicate by check mark whether the registrant ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days . Yes No Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Website , if any , every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S - T ( §232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit and post such files ) . Yes No Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , or a smaller reporting company , or an emerging growth company . See the definitions of " large accelerated filer , " " accelerated filer " and " smaller reporting company , " and " emerging growth company " in Rule 12b - 2 of the Exchange Act . Large accelerated filer > Accelerated filer Non - accelerated filer Smaller reporting company Emerging growth company On November 12 , 2021 , 53,885,546 shares of the registrant's common stock were outstanding . If an emerging growth company , indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to section 13 ( a ) of the Exchange Act . Indicate by check mark whether the registrant has filed a report on and attestation to its management's assessment of the effectiveness of its internal control over financial reporting under Section 404 ( b ) of the Sarbanes - Oxley Act ( 15 U.S.C. 7262 ( b ) ) by the registered public accounting firm that prepared or issued its audit report . Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Act ) . Yes No The aggregate market value of the registrant's common stock held by non - affiliates on March 28 , 2021 , was $ 7.1 billion ( based upon the closing price of a share of registrant's common stock as reported by the Nasdaq National Market on that date ) . DOCUMENT INCORPORATED BY REFERENCE Portions of registrant's Proxy Statement for its 2022 Annual Meeting of Stockholders are incorporated by reference in Part III of this report where indicated .