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EXHIBIT 23

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

      We hereby consent to the incorporation by reference in the Registration Statements on Form S-8 (Nos. 333-148712, 033-94706, 333-11757, 333-53036, 333-85558, 333-145201 and 333-145199) of Tetra Tech, Inc. of our report dated November 18, 2008 relating to the financial statements, financial statement schedule and the effectiveness of internal control over financial reporting, which appears in this Form 10-K.

/s/ PRICEWATERHOUSECOOPERS LLP

Los Angeles, California
November 18, 2008

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EXHIBIT 23

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM