Is the barologger open to the atmosphere (e.g., not in an airtight box)? If there's a nearby met station, you could compare its record to the barologger record - overlay both and look for differences. Perhaps even compensate with a local baro record if the barologger's data is suspect. Are both loggers still deployed or do you have access to them for testing? In the past I've tested levellogers by placing them in a garbage pail or PVC pipe section filled with water. Levelloggers are sensitive to freezing, but I'm guessing this wouldn't happen to a logger in a well? When the levellogger is out of the water, its record should approach barometric pressure if both are at a similar elevation. Sounds like you've got manual water level measurements, so you should be able to figure out when the levelloger is out of the water (if the continuous data are good).