EXHIBIT 10.20 INDEMNITY AGREEMENT

EXHIBIT 10.20

INDEMNITY AGREEMENT

        THIS INDEMNITY AGREEMENT (this "Agreement") dated as of                        , 2004, is made by and between Tetra Tech, Inc., a Delaware corporation (the "Company"), and                        (the "Indemnitee").

R E C I T A L S:

        A.    The Company recognizes that competent and experienced persons are increasingly reluctant to serve as directors and officers of corporations unless they are protected by comprehensive liability insurance or indemnification, or both, due to increased exposure to litigation costs and risks resulting from their service to such corporations, and due to the fact that the exposure frequently bears no reasonable relationship to the compensation of such directors or officers.

        B.    The statutes and judicial decisions regarding the duties of directors and officers are often difficult to apply, ambiguous or conflicting, and therefore fail to provide such directors with adequate, reliable knowledge of legal risks to which they are exposed or information regarding the proper course of action to take.

        C.    The Company and the Indemnitee recognize that plaintiffs often seek damages in such large amounts and the costs of litigation may be so substantial (whether or not the case is meritorious), that the defense and/or settlement of such litigation is often beyond the personal resources of directors and officers.

        D.    The Company believes that it is unfair for its directors and officers to assume the risk of substantial judgments and other expenses which may occur in cases in which the director and/or officer, as the case may be, received no personal profit and in cases where such person acted in good faith.

        E.    Section 145 of the General Corporation Law of Delaware ("Section 145"), under which the Company is organized, empowers the Company to indemnify its directors and officers by agreement and to indemnify persons who serve, at the request of the Company, as the directors and officers of other corporations or enterprises, and expressly provides that the indemnification provided by Section 145 is not exclusive.

        F.    The Board of Directors of the Company has determined that contractual indemnification as set forth herein is not only reasonable and prudent but necessary to promote the best interests of the Company and its stockholders.

        G.    The Company desires and has requested the Indemnitee to serve or continue to serve as a director and/or officer of the Company.

        H.    The Indemnitee only is willing to serve, or to continue to serve, as a director and/or officer of the Company if the Indemnitee is furnished the indemnity provided for herein by the Company.

A G R E E M E N T:

        NOW THEREFORE, in consideration of the mutual covenants and agreements set forth below, the parties hereto, intending to be legally bound, hereby agree as follows:

        1.    Definitions.

        (a)    Agent. For purposes of this Agreement, "agent" of the Company means any person who: (i) is or was a director and/or officer of the Company or a subsidiary of the Company; or (ii) is or was serving at the request of, for the convenience of, or to represent the interest of the Company or a subsidiary of the Company as a director, officer or trustee of, or in any other capacity with, another foreign or domestic corporation, partnership, joint venture or employee benefit plan.

        (b)    Expenses. For purposes of this Agreement, "expenses" includes all direct and indirect costs of any type or nature whatsoever (including, without limitation, all attorneys' fees and related disbursements, other out-of-pocket costs and reasonable compensation for time spent by the Indemnitee for which he is not otherwise compensated by the Company or any third party, provided that the rate of compensation and estimated time involved is approved in advance by the Board of Directors of the Company), actually and reasonably incurred by the Indemnitee in connection with either the investigation, defense or appeal of a proceeding or establishing or enforcing a right to indemnification under this Agreement, Section 145 or otherwise, and amounts paid in settlement by or on behalf of the Indemnitee, but shall not include any judgments, fines or penalties actually levied against the Indemnitee.

        (c)    Proceedings. For the purposes of this Agreement, "proceeding" means any threatened, pending, or completed action, suit, arbitration, hearing or other proceeding, whether civil, criminal, administrative, investigative or any other type whatsoever.

        (d)    Subsidiary. For purposes of this Agreement, "subsidiary" means any corporation of which more than 50% of the outstanding voting securities are owned directly or indirectly by the Company, by the Company and one or more other subsidiaries, or by one or more other subsidiaries.

        2.    Agreement to Serve. The Indemnitee agrees to serve and/or continue to serve as an agent of the Company or a subsidiary of the Company, at the will of such corporation (or under separate agreement, if such agreement exists), in the capacity the Indemnitee currently serves as an agent of such corporation, so long as the Indemnitee is duly appointed or elected and qualified in accordance with the applicable provisions of the Bylaws of such corporation or of any subsidiary thereof, or until such time as the Indemnitee tenders his resignation in writing; provided, however, that nothing contained in this Agreement is intended to create any right to continued employment of the Indemnitee in any capacity or to give the Company the right to require the Indemnitee to resign from the Board of Directors of the Company. This Agreement shall continue in force after the Indemnitee has ceased to serve as a director or officer of the Company.

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        3.    Indemnification.

        (a)    Indemnification in Third Party Proceedings. Subject to Section 10 below, the Company shall indemnify the Indemnitee if the Indemnitee is a party to or threatened to be made a party to or otherwise involved in any proceeding (other than a proceeding by or in the name of the Company to procure a judgment in its favor) by reason of the fact that the Indemnitee is or was an agent of the Company, or by reason of any act or inaction by him in any such capacity, against any and all expenses and liabilities of any type whatsoever (including, but not limited to, judgments, fines and penalties), actually and reasonably incurred by him in connection with the investigation, defense, settlement or appeal of such proceeding, but only if the Indemnitee acted in good faith and in a manner he reasonably believed to be in, or not opposed to, the best interests of the Company, and, with respect to any criminal action or proceeding, had no reasonable cause to believe Indemnitee's conduct was unlawful, pursuant to the presumption set forth in subsection (c) below, as applicable. The termination of any proceeding by judgment, order of court, settlement, conviction or on plea of nolo contendere, or its equivalent, shall not, of itself, create a presumption that the Indemnitee did not act in good faith in a manner which he reasonably believed to be in, or not opposed to, the best interests of the Company, and with respect to any criminal proceedings, that such person had reasonable cause to believe that his conduct was unlawful.

        (b)    Indemnification in Derivative Actions. Subject to Section 10 below, the Company shall indemnify the Indemnitee if the Indemnitee is a party to or threatened to be made a party to or otherwise involved in any proceeding by or in the name of the Company to procure a judgment in its favor by reason of the fact that the Indemnitee is or was an agent of the Company, or by reason of any act or inaction by him in any such capacity, against all expenses actually and reasonably incurred by the Indemnitee in connection with the investigation, defense, settlement, or appeal of such proceedings, but only if the Indemnitee acted in good faith and in a manner he reasonably believed to be in, or not opposed to, the best interests of the Company, pursuant to the presumption set forth in subsection (c) below; provided, however, that no indemnification under this Section 3 shall be made in respect of any claim, issue or matter as to which the Indemnitee shall have been finally adjudged to be liable to the Company by a court of competent jurisdiction due to willful misconduct of a culpable nature in the performance of the Indemnitee's duty to the Company, unless and only to the extent that any court in which such proceeding was brought shall determine upon application that, despite the adjudication of liability but in view of all the circumstances of the case, such person is fairly and reasonably entitled to indemnity for such expenses as such court shall deem proper.

        (c)    Conclusive Presumption Regarding Indemnitee Conduct. With respect to Sections 3(a) and 3(b) above, the Indemnitee shall be conclusively presumed to have acted in good faith and in a manner Indemnitee reasonably believed to be in, or not opposed to, the best interests of the Company, and, with respect to any criminal action or proceeding, to have had no reasonable cause to believe Indemnitee's conduct was unlawful, unless a determination is made that the Indemnitee has not acted in accordance with the standards set forth above (i) by the Board of Directors by a majority vote of a quorum thereof consisting of directors who were not parties to the proceeding due to which a claim is made under this Agreement, (ii) by the stockholders of the Company by a majority vote of stockholders who were not parties to such a proceeding, or (iii) in a written opinion of independent legal counsel, selection of whom has been approved by the

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Indemnitee in writing or, if not so approved, then approved by a panel of arbitrators, one of whom is selected by the Company, another of whom is selected by the Indemnitee and the last of whom is selected by the first two arbitrators so selected.

        4.    Indemnification of Expenses of Successful Party. Notwithstanding any other provisions of this Agreement, to the extent that the Indemnitee has been successful on the merits or otherwise in defense of any proceeding or in defense of any claim, issue or matter therein, including the dismissal of any action without prejudice, the Company shall indemnify the Indemnitee against all expenses actually incurred in connection with the investigation, defense or appeal of such proceeding.

        5.    Partial Indemnification. If the Indemnitee is entitled under any provision of this Agreement to indemnification by the Company for some or a portion of any expenses or liabilities of any type whatsoever (including, but not limited to, judgments, fines or penalties) actually incurred by him in the investigation, defense, settlement or appeal of a proceeding but is not entitled, however, to indemnification for the total amount thereof, the Company shall nevertheless indemnify the Indemnitee for the portion thereof to which the Indemnitee is entitled.

        6.    Advancement of Expenses. Subject to Section 10(b) below, the Company shall advance all expenses incurred by the Indemnitee in connection with the investigation, defense, settlement or appeal of any proceeding to which the Indemnitee is a party or is threatened to be made a party by reason of the fact that the Indemnitee is or was an agent of the Company. The Indemnitee hereby undertakes to repay such amounts advanced only if, and to the extent that, it shall ultimately be determined that the Indemnitee is not entitled to be indemnified by the Company as authorized by this Agreement. The advances to be made hereunder shall be paid by the Company to or on behalf of the Indemnitee within 30 days following delivery of a written request therefor by the Indemnitee to the Company.

        7.    Notice and Other Indemnification Procedures.

        (a)    Notification of Proceedi