Tetra Tech Wins 5-year $38.7 Million EPA OSWER Contract

Date: September 7, 2007

Source: Tetra Tech, Inc.

Tetra Tech Wins $38.7 Million EPA OSWER Technology Transfer and Training Support Contract

Tetra Tech, Inc. (NASDAQ: TTEK) announced today that it has been awarded a $38.7 million contract to provide technology transfer and training support for the U.S. Environmental Protection Agency's (EPA) Office of Solid Waste and Emergency Response (OSWER). Tetra Tech will provide scientific, engineering, and management consulting services to support the Superfund Program and other EPA waste management programs including solid waste, emergency management, underground storage tanks, and brownfields programs. The cost-plus fixed-fee contract has a period of performance of five years.

Tetra Tech will provide expertise in a full range of assessment and cleanup technologies, from emerging technologies to established methods for addressing hazardous waste cleanup and emergency response. Tetra Tech will deliver advisory and technical assistance to site managers supporting characterization, remedial design, remedial optimization, and land revitalization. Tetra Tech will also assist EPA in preparing and conducting national and international state-of-the-practice training on scientific and technical issues related to emergency response and remediation of sites, appropriate assessment, and integration of innovative technologies into site cleanup plans.

This contract is an expansion of work that Tetra Tech has been performing for the Office of Superfund Remediation and Technology Innovation (OSRTI).

About EPA OSRTI (www.epa.gov/superfund)

The mission of the OSRTI technology and training program is to provide world-class technology information and expert field and laboratory support to customers who respond to emergency releases of hazardous materials and manage longer-term site assessment and remediation projects. As national and international leaders in innovation for laboratory, field, and remediation practices, OSRTI identifies, develops, evaluates, and advocates promising state-of-the-art technologies, innovative business practices, and tools for streamlining and improving the cost effectiveness and performance of assessment and cleanup strategies.

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.

For more information, contact:
Jorge Casado
Investor Relations
Tetra Tech, Inc.
Talia Starkey, Media & Public Relations

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