For a drainfield to work the water has to be able to flow out of it into the ground and be absorbed by the ground. The perc test checks the ground to determine its feasibility. IF the ground is soaked, then there is no way the water can drain OUT of the pipe, and even worse, the water in the ground WILL ENTER the pipe and may flood the septic tank and possibly your house drainage piping depending on relative elevations. If the old system really failed, and he was not just trying to make some money by installing a new field, then it will not work now either. I question the wisdom of putting a field in an area which would obviously be flooded, and wonder how he ever got a permit to put it there, unless he did the test during a dry spell, and no one checked the terrain.