Logging samples involves a whole series of field tests and observations. Some of them are straightforward and reproducible as long as you use the correct procedure. Visual observations, however, tend to vary by the individual. Are you a "grouper" or a "splitter" when you see different layers? When was the last time you calibrated your internal sense of what a particular grain size looks like?
The environmental biz tends to have a revolving cast of characters, and often, the training to standardize field observations misses a significant portion of the group because they're out in the field on some sort of time-critical (and billable!) project. And although the soil texture and other geological observations are important when you're trying to figure out where contamination is going, they're generally not considered to be as critical as the chemical data. So unless a high-level geologist pushes for training and standardization across the organization on a regular basis, the field staff tend to develop their own methods of transcribing what they're seeing.
If I'm reviewing field soil logs, consistency is key. It's far easier to figure out what the stratigraphy is like if the project had a single geologist, or just a few. Or, if someone actually has a discussion about what they're seeing and the group agrees that they're going to call this greenish-gray color "olive" and that this friable, gray-white stuff is indeed fly ash.
What usually happens is that the site has a long history, with several different contractors poking holes in different areas depending on what was found in the last phase, the budget, and changes in regulations. So when I need to write a report and pull in all these different logs to develop a complete picture of a site, I have to decide if this "till" is the same material as this "sandy silt" and whether we have a rainbow of different units or someone was colorblind. Not everybody writes their observations, either.
All this matters because I'm trying to extrapolate between logs. Do we have continuous units that are consistent barriers to contamination migration? If a particular unit always has a certain chemical signature, can we find it again if we go back to the site without spending a fortune in analytical costs? Now, if I could only convince the rest of the field staff to think "big picture" when they're out there in adverse conditions...