If you decide to let them use gravel, ask for a filter fabric wrap like Mirafi 140N. This is not an uncommon request (necessary if large excavation), but the cost of the labor will encourage him to change to sand.
Big doubt that drawdown of aquifer at +-150' is your residential problem. 99/100 times it is soil movement. You need more data. Pits are easiest, cores are easy. Be prepared to be baffled for a long time on where moisture souce is, sometimes several consultants work on the same house before...
