French drains. Rock in trenches, or even perforated 4 inch PVC laid on top of the rocks, will catch and carry away water permanently. Raise the foundation so you have a downhill slope all around to carry rain water away from the base of the structure. If the structure runs across an underground water line, I'd consider a different location or rerouting the line. Having struggled with irrigation for nearly two decades here in the desert, almost all of my main irrigation lines are now schedule 80 PVC, very long life, not easily broken or breached. More expensive, but fewer problems.
My property is higher on both ends and shallow in the middle by 3 feet. My outside irrigation leads to open sprinklers and dribblers in the low areas, so when I cut off the water, the pipes all drain so even with a deep freeze,the buried pipes have nothing to freeze and burst the pipe.
Mentioning all this because for the wet spot to recur, suggests that a drain will be necessary. I'd also make sure you have rain gutters that carry the water away from the building. We have a complication of having a layer of concrete-like caliche, which doesn't let water soak down. Had to dig 2-4 feet down to enable planting and drainage.
I futzed around with schedule 40 for years because it was cheaper. It was always bursting, leaking, giving me fits and costly repairs. Schedule 80 is almost three times the price, but careful design, trenching and the self draining via gravity, has made it trouble free. I have risers here and there that feed short drip tubing, but also reveal the location of every pipe. A 1 day water leak here jumps the water bill by $300-$500. That has not happened since putting in the schedule 80.
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