Groundwater & Basement Water Intrusion in Skokie, IL

Because elevation relative to the sewer decides it, and that does not change. The houses whose basement floor drains sit lowest on a given sewer segment are the relief points when the system surcharges, and they will be the relief points every time. Nothing about the individual house is defective. A backwater valve changes the outcome for that property specifically, which is why it is the standard remedy rather than any amount of exterior work.

Assume it will get wet again and set it up accordingly. That means a backwater valve if there is not one, mechanicals raised off the floor, and no storage of anything valuable at floor level. If the space is being refinished after an event, materials that tolerate wetting, and a floor system that can be lifted rather than replaced, make the next event a cleanup rather than a reconstruction. This stock has a known failure mode and it is worth designing around it.

It explains the water table, which is the part most owners find puzzling. This ground was marsh, and it is dry because of ditching and drainage works rather than because it sits high. The natural tendency of the soil is to hold water, and the seasonal table comes up close to basement floor level in wet periods. That is why basements here weep in spring without any storm event, and why exterior sealing alone rarely resolves it.