Well, it looks like they used PVC pipes. While much of the drainage system is probably insulated, the areas used for collection are most likely not, which would cause a backup. Also, I didn't find any good depths for which the pipes are buried, but frost level in Chicago can get rather deep. 4-6 feet, and I don't think they buried them down that far. Last thought, right field is backing up, which is also where the drainage tank is. The drainage tank might be closed to prevent the tank from cracking due to permafrost. I'm no expert, but I've taken a few classes relative to this.