If you have water seeping out, you need to get it checked. It should not be doing that. Your county health department can probably test a sample to see if it is contaminated or not. It’s something I’d make a priority.
The way a septic tank works is that it is filled with microbes that digest the waste going into it, leaving you some solids that sink to the bottom and what is supposed to be clean water leaving it. Most of what goes in gets converted into water and gasses by those microbes, even the solids. That’s why you can go years without having to get a properly sized and properly working septic tank pumped.
In theory, if the septic system is working right, what goes out of the tank is clean water. It can go into the environment without polluting the environment. It’s the same principle a sewage treatment plant uses. If a sewage treatment plant is designed right and working right, it puts clean water out and it does not smell. I think we all know that doesn’t always happen. Septic systems don’t always operate right either. It may not be designed or installed right, it may need to be pumped, or something may be plugged. That’s why you need to get that water sample coming to the surface tested, not just for the health of your chickens but for your health.
I’ve got the situation here that the people that built this house put the field lines real close to a low area I call The Bog. It has a wet weather seep in it that often has standing water in it during wet weather. I had that standing water tested. It’s clean so the septic is working right.