A long time ago, I mentioned that field personnel in environmental consulting can be broken into 3 broad categories, which are about evenly represented: geologists, engineers, and environmental scientists.
Everyone starts out doing environmental sampling, because those samples are the foundation of everything else we do. And the cheap, entry-level folks get to do the grunt work. Field folks have a relatively clear pathway to management: first, start
running small field events, then more complex field events, then entire
projects. There's enough fieldwork and non-scientific
logistics/management in the industry that you don't need to be an expert
in what you actually went to school for to be successful as a manager.
But some people don't want to be managers, or there are too many managers around already. So they specialize.
Over time, the geologists start to focus on more technical geology work (overseeing drill rigs and field projects of increasing complexity, evaluating geologic data) and the engineers likewise start to do more engineering analysis. Some of the environmental scientists are chemists or biologists, and they may end up focusing on data validation, risk assessments, or ecology-type work (wetlands delineation, etc). Other environmental scientists are generalists: either they majored in Environmental Science or their academic focus was in something not all that helpful for environmental consulting. Options for specialization include regulatory compliance, hazardous material management, and industrial hygiene/safety.
Career paths in environmental consulting are not static, but are generally ad-hoc and carved out of a combination of technical skills, the projects available, and how much you're able to push into the role you want.