Pros
Tt is a huge company that is made up of smaller groups that are further split into smaller companies that are considered separate cost centers. It is great because you can sometimes get opportunities to work on huge projects in exotic places but also feel like you work for a very small one office company with very localized talents and projects. From the junior level up through the staff level there is a very hands off approach from the company and it is left entirely up to the project managers on what kind of work environment you will have. With the right PM and the right project Tt is a great place to work.
Cons
Because of the separation between offices, companies, and groups it is exceedingly difficult to work to win very large projects. There is also a very large disconnect between those out there doing the work and the number of people who are office staff and supporting them off of a project raises costs. These issues pale in comparison to Tetra Tech's largest flaw. They do not respect or support their employees. After many years of billable work the first sign of a gap in projects they furlough you using the overtime hours you have accrued. Employees not directly related to winning projects, ie junior employees and field staff are required to find their own work when sr, projet managers do not have work for them. They don't allow you to bill for work that is part of doing a job, they require you to travel on your own time and they have continuously rolled back benefits and put up roadblocks to getting a job done. Overtime it is easy to accept these quality of life rollbacks but eventually it results in Tt losing contracts because of costs, losing employees to competitors, and the degradation of employee enthusiasm and drive.