THE PILOT REPORTED A LOSS OF ENGINE POWER SHORTLY AFTER TAKE OFF AT AN ALTITUDE ESTIMATED AS 200-300' AGL. THE AIRPLANE LANDED HARD IN A FIELD ADJACENT TO THE DEPARTURE RUNWAY, RESULTING IN SUBSTANTIAL DAMAGE TO THE AIRPLANE AND MINOR INJURIES TO ITS OCCUPANTS. A POST CRASH INSPECTION OF THE AIRPLANE REVEALED A CONSIDERABLE AMOUNT OF VISIBLE SEDIMENT IN THE FUEL SYSTEM. THE ENGINE RAN NORMALLY ONCE FRESH FUEL WAS ADDED.