Storm service lateral backups can be caused by a lack of maintenance to your gutters and downspouts. Leaves and debris often clog gutters and only allow a low flow of water to the downspouts. The overflow of water from blocked gutters, misaligned downspouts, missing or damaged gutters will allow the water to enter the home along the foundation wall. The soil surrounding your home becomes saturated and the water may penetrate cracks in the walls and the floor of the basement.
The service laterals can also be blocked by roots. Blocked storm water in service laterals will cause backup in footer drains and will also exit (force its way out) the storm laterals and enter the sanitary service laterals through cracks and joint separation. The sanitary laterals are always at a lower elevation so they collect the water that exits the storm sewer laterals.