I have worked for a company full of hydrogeologists.
I would say that a company that has remote jobsites would usually provide vehicles, since travel might be on rough roads, require four wheel drive, and need a variety of large/dirty tools to be transported, and employees can't be assumed to have vehicles capable of that kind of rigorous use.
At the same time, arrangements can usually IMO be made to use a personal vehicle when it's at the preference of the employee. For example if he wanted to take a few days of personal time after this job, and preferred to leave straight from the jobsite since it was closer to wherever he was going (not implying this, it's a purely fictional scenario, just as example), he could likely get permission to use his personal vehicle for that day and get reimbursed by the mile as
@Knox suggests.
This could work especially well if there was another employee at the jobsite with him, in a company vehicle which could carry all the needed tools/machinery etc.
Somewhere upthread someone said he was taking groundwater samples? Do we actually know that or was someone guessing? I have done that and it involves going to existing monitoring wells and lowering a bailing device down inside, and then properly extracting, bottling and labelling the water retrieved from each well.
When I did this it was not a job that required two people -- but perhaps if the site was sufficiently remote, or was along the route to another jobsite, it was deemed best to have a second person there. Or maybe the other person was new and being trained...
As it was done in the late 80s (am I out of date yet?) groundwater sampling and the attendant labelling and paperwork took maybe 15-20 minutes per well. So if this was what he was doing, it was not likely an all-day job unless there were many wells.
Regarding the Phase I/II/III Site Assessments mentioned above -- I was trained to do the Phase I reports and they generally involved only a few hours at most on site, though I suppose large acreages might take days to fully inspect. The Phase I report is basically a deep history of the site to determine if there is any indication on the ground, or history to suggest that toxic hazards that may have gotten into the soil or groundwater. (A few hours on site was usually enough but then many hours of research at the Recorder's Office and looking at historical aerial photos were also needed.)
It's possible that the higher levels of site assessments might involve soil samples, digging, more of a geologic assessment, I can't really say. I was doing this in an urban area where the concern was over previous human uses of the parcel in question, but it sounds like this jobsite was open desert land that had never been developed? Maybe it had become an unintended dumping ground or something along those lines?
My experience and opinion only...
