Pros
If you have a manager that cares, or people to train you , your knowledge will grow, but many get lost in the system and basically have to train themselves in a field where that isn't exactly the best idea. You can create great connections with other companies that often end up employing former TEI employees. Learn a wide variety of waste management at many different types of locations (healthcare, manufacturing, etc.)
Cons
Very poor pay, cliques of employees are formed which can affect where you work and your pay. Overtime is expected. Training for some is basically non existent beyond required federal training. Schedules are changed last minute which means you never know when you are supposed to be there or when you might leave. Very non-diverse workplace and it really shows. Forced formal holiday parties that are not compensated. If you ever take a job at a competitor (TEI is pretty ubiquitous in the greater Boston area) TEI will probably threaten to sue you. Even if your accepted job really had nothing to do with what you did for TEI. Pressure to spend even more of your time at after work events either sponsored or not and refusal, even with a valid excuse, is noted by them for sure.