Tetra Tech Wins $15 Million 
EPA Water Contract

PASADENA, CA (10/26/06) -- Tetra Tech, Inc. (NASDAQ:TTEK) announced today that it has signed a $15 million contract with the U.S. Environmental Protection Agency (EPA) to provide technical support to the Pacific Southwest Region (Region 9) Water Division as they implement their core water programs, including programs associated with the Clean Water Act, Marine Protection and Sanctuaries Research Act, and Safe Drinking Water Act. The contract has a four-year period of performance and will include time and materials and fixed-price tasks.

This contract expands Tetra Tech's technical support for EPA's west coast watershed and coastal protection programs. It will provide an important opportunity for EPA and its state, territory, and tribal partners to continue core water program integration and fully utilize the watershed approach to address challenging water pollution problems.

About EPA Region 9 Water Division (www.epa.gov/region9/water)

EPA Region 9 serves the Pacific Southwest, including Arizona, California, Hawaii, Nevada, the Pacific Islands, and Tribal Nations. The Water Division is responsible for providing clean and safe surface water, groundwater, and drinking water and protecting and restoring aquatic ecosystems. They oversee state and tribal implementation of core programs to accomplish these goals and they encourage use of a watershed approach to protect public health and water resources including lakes, rivers, estuaries, oceans, and wetlands.

About Tetra Tech (www.tetratech.com)

Tetra Tech is a leading provider of consulting, engineering, and technical services. With approximately 7,500 associates located in the United States and internationally, the Company supports commercial and government clients in the areas of resource management and infrastructure. Tetra Tech's services include research and development, applied science and technology, engineering design, program management, construction management, and operations and maintenance.

Any statements made in this release that are not based on historical fact are forward-looking statements. Any forward-looking statements made in this release represent management's best judgment as to what may occur in the future. However, Tetra Tech's actual outcome and results are not guaranteed and are subject to certain risks, uncertainties and assumptions ("Future Factors"), and may differ materially from what is expressed. For a description of Future Factors that could cause actual results to differ materially from such forward-looking statements, see the discussion under the section "Risk Factors" included in the Company's Form 10-K and 10-Q filings with the Securities and Exchange Commission.