Tetra Tech (TTEK)

RECITALS:

A.            The Borrower, the lenders party thereto (the “Existing Lenders”) and Bank of America, N.A., as administrative agent under the Existing Credit Agreement (defined below) (in such capacity, the “Existing Agent”), are parties to that certain Amended and Restated Credit Agreement dated as of July 21, 2004 (which amended and restated that certain Credit Agreement dated as of March 17, 2000 by and among the Borrower, the Existing Agent and certain lenders party thereto), as amended by (i) that certain First Amendment dated as of December 14, 2004, (ii) that certain Second Amendment dated as of May 12, 2005, and (iii) that certain Third Amendment dated as of March 24, 2006 (as so amended, the “Existing Credit Agreement”), pursuant to which the Lenders have made available to the Borrower a revolving credit facility in an aggregate principal amount (as of the date hereof) of up to $150,000,000, including a letter of credit subfacility and a swing line subfacility.

B.            The Borrower has requested that the Existing Credit Agreement be further amended and restated in order to, among other things, (a) extend the maturity date of the revolving credit facility, (b) increase the maximum aggregate principal amount of the revolving credit facility to $300,000,000, and (c) make certain other amendments to the Existing Credit Agreement.

C.            The parties hereto are willing to so amend and restate the Existing Credit Agreement upon the terms and conditions set forth herein.

In order to facilitate the amendment and restatement of the Existing Credit Agreement and in consideration of the mutual covenants and agreements herein contained, the parties hereto agree as follows: