Lots of exhaustive research and investigating,and determination.They used a well drilling rig to bring up soil samples if I recall.I highly recommend the book Treasure in A Cornfield
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In 1987, Bob Hawley and his sons, Greg and David, set out to find the boat. The Hawleys used old maps and a proton
magnetometer to figure out the probable location, and finally discovered the
Arabia half a mile from the river and under 45 feet (14 m) of silt and topsoil.
The owners of the farm gave permission for excavation, with the condition that the work be completed before the spring planting. The Hawleys, along with family friends Jerry Mackey and David Luttrell, set out to excavate the boat during the winter months while the water table was at its lowest point. They performed a series of drilling tests to determine the exact location of the hull, then marked the perimeter with powdered chalk. Heavy equipment, including a 100-ton crane, was brought in by both river and road transport during the summer and fall. 20 irrigation pumps were installed around the site to lower the water level and to keep the site from flooding. The 65-foot-deep (20 m) wells removed 20,000 US gallons (76,000 l) per minute from the ground. On November 26, 1988, the boat was exposed. Four days later, artifacts from the boat began to appear, beginning with a
Goodyear rubber overshoe. On December 5, a wooden crate filled with elegant china was unearthed. The mud was such an effective preserver that the yellow packing straw was still visible. Thousands of artifacts were recovered intact, including jars of preserved food that are still edible. The artifacts that were recovered are housed in the Steamboat Arabia Museum.[SUP]
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On February 11, 1989, work ceased at the site, and the pumps were turned off. The hole filled with water overnight.
