not enough space error copying files to icloud drive

When I try to copy a folder from a local external drive to iCloud Drive I receive an error message that there is not enough space. There is plenty of space on iCloud Drive for the folder (4x the size of the folder). I experimented a bit and found I was limited to the amount of free space on my boot drive. Once I broke it up into smaller pieces I was able to copy the folder over. As I did this it consumed space on my boot drive. I assume it made a ghost copy to use as it uploaded the files. That space has not been freed up more than a week after the file copy. How do I reclaim this space?