Occasionally I hit these projects when they are in old portions of the city. You have to time it perfectly and usually only get one or two shots at it. They started this yesterday, I hit it last night, and today it's all gravel!
I found one nice bar token, a small bottle about 3" tall and other interesting items.
The bottle reads: 30 Phenolax Wafers Upjohn
If you are real lucky and in real old parts of town, the equipment can dig up and expose privys and bottles can be found.
The rest is buried for another 80 years!