When a pump system isn't holding pressure it usually means that there is a leak or that the foot valve is clogged or faulty. All it takes is a pinhole-sized leak to bring your system down. Your local well company can pressure-check the system for holes and usually make the proper repair in a few hours. If all or part of the system is new it is probably still under warranty. Keep in mind that most warranty repairs are free. By the way, the fact that your supply line rests on four inches beneath the surface scares us. It should have been laid at least eighteen-inches below grade. The reason ? shallow pipes are often damaged during annual and semiannual cultivation. If it were our system we would rethink the shallow depth.