A source of infiltration in a collection system is:

Infiltration in a collection system refers to the unintentional entry of groundwater into the sewer system through cracks, joints, or other openings. Broken pipe joints represent a significant source of infiltration because they can allow groundwater to seep into the sewer system, leading to issues such as increased flow that might overwhelm treatment capacities and increase treatment costs.

When pipe joints are compromised, the structural integrity is diminished, making it easier for surrounding groundwater to enter the pipes. This issue is particularly prevalent in aging or poorly maintained systems where leaks may develop over time.

The other options listed do not typically contribute to infiltration. New pipes are less likely to have infiltration if properly installed. Proper joint pipes are designed to fit tightly to prevent leaks. Pipe liners are often used as a method of rehabilitation to seal leaks and prevent ingress, thus reducing the risk of infiltration.