I started out doing the basic geology stuff (I was going to say "scutwork", but that's not fair or even very accurate) everyone in environmental consulting will recognize - watching drill rigs, collecting samples of all different environmental media, from rock cores to groundwater to
I found my calling when I started to write reports - how did the contamination get where it is, and where is it going? And where is it, exactly, since I'm triangulating between a couple wells at different depths that were put in as an afterthought because we thought the contamination was somewhere else when we started. In order to answer those questions, I had to know a lot about groundwater flow paths (that can be a dissertation in irregularly fractured bedrock), affinity of the contaminant to the solid material, and the geochemistry that may encourage the local bugs to degrade it into something more (or less!) innocuous.
I went to grad school to learn more about that stuff, and after I graduated, I continued to design projects to get those answers to the degree needed by the budget, the regulatory requirements, and the other resources available. Some of the knowledge I've gained has been more chemistry or biology or engineering, but a lot of it has been pure geology: geomorphology, hydrogeology, mineralogy.
One thing I don't know well is the overall structural geologic history of the areas I've worked in. Sure, I have a general sense that this material got all smushed up when a chunk of another continent smeared into the North American plate, and this major fracture bisects that unit but not the one next to it and they both were raised up and eroded and now what you see on the ground is a mess. And I know the names of the local formations, primarily because they're in reports I've read or written.
So if you're out in the field for an inspection/don't want to be in the office because it's a nice day and you think we'll be bringing up some cool rocks, and you ask me what the age of the rocks at my site are, I don't have a clue. Suggesting, "are those part of the XYZ group?" will help in that I can hem and haw about XYZ group, which I may have remembered from another report a long time ago. Doesn't mean I'm a bad geologist, just that I'm focused on something else.