From what I understand on news reports, the bee population was seriously reduced this winter and spring. There is a lot of speculation as to what happened to them but the common thought is with the mild winter and hard freezes that most areas saw, the bees just didn't make it back to hives in time to avoid the cold. There are a lot less bees in my yard and fruit growers here are renting hives from bee keepers. I would go ahead and move your sand, I don't think they are coming back. Sorry

Bee's are going missing everywhere. The only answer is fro you yourself to keep bees or grow bee loving plants and provide houses for them!
SAVE THE BEES!

Make sure to read up on how to treat them for mites and their other diseases, though, or you will do more harm than good. Bees are getting harder to keep healthy due to new problems with insecticides and a new mite that kills them off.

There is some educational and interesting info on miner bees at North Carolina State University. See link below
www.ces.ncsu.edu/depts/ent/notes

Thank you all for replying. I guess I will spread the sand/dirt but provide another pile elsewhere in my yard in hopes miner bees will return. (sigh) On a positive note the bumblebees have returned, for a second year, to the hive in an old, large birdhouse on my front porch. YAY!