A lot of good posts. So thank you, keep them coming. I'll see if I can add more info to address some and maybe it'll help direct me even more.
So, I say it drains okay. By that I mean, if I can get a week without rain, the mud dries up pretty well and I can go walk on it without sinking in at all. And it appears dry.
BUT. A big but too. I live in Western Washington. Enumclaw to be specific. Fall through spring it rains an average of 6 days/week.
I live on 5 acres, I'd say 2.5 is currently usable that I can eventually add more paddocks/cross fencing after I fully fence our property. The other 2.5 acres is trees or our living areas. Eventually the plan IS to make 3 or 4 of these paddocks to rotate them through.
We had 2 horses and a pony...
But a month ago my in-laws brought their 32 year old mare over "temporarily" while they worked on moving to Arizona, then decided they didn't think she'd survive the trip or heat down there, so now they're basically leaving her for us to take care of. So now its 4 sets of hooves.
Additional question. When you guys mention subsoiling through the hardpan... I live on a very rich aquifer. I almost wonder if parts of my property are above a spring. I've never dried my well up and have accidentally left the hose on 12 hours in the summer, I don't have a water tank on my well system. If I subsoil through the hardpan.... will that actually help it drain? Or would it just introduce more water from below? I'm not sure how that works.
The areas the horses dont walk in much are pretty dry and hard even through the rain, it's really just their main leisure areas. By the gates, shed front half of paddocks. The back halves they only walk around enough to finish off whatever grass may be popping up.