When I built the last shed ( 50 by 60) most companies were talking about sinking the poles 8 ft in the ground. The guys I hired only sunk them in 5 ft. When I asked why not deeper, the guy asked at what level I start hitting water in the yard. I replied "About 8 ft." As the light bulb came on, he asked me why I'd want to put a building on mud. They drill 6 ft and put a foot of screened rock in the hole before the pole for drainage. Up here any frost in the ground will cause the poles to shift up, so the crushed rock keeps the water away from the poles. Might be too late to change what you have, but something to keep in mind for next time.