Information on the soil/ground – you can get this from a soils report, asking neighbors, and/or firsthand knowledge gained with a shovel on site. Also distance to groundwater and any quality information, especially from anyone with wells in the area. Same goes for septic systems re: sewage disposal. Proximity to any hazardous materials/waste sites and/or spills is also good to check out. EPA’s websites have major HazWaste sites identified online, I believe, and you can also find out where major users/storers of hazmat are in the area there as well. Finally, check the local government websites to gauge how their ordinances are re your planned activities.