traffic on roadways above the sewer, careless construction practices in nearby trenches, or degradation of the sewer pipe materials. In general, volume of leakage will increase over time. Damaged and broken sewer cleanouts are a major cause of infiltration into municipal sewer systems.

Infiltration will occur where local groundwater elevation is higher than the sewer pipe. Gravel bedding materials in sewer pipe trenches act as a French drain. Groundwater flows parallel to the sewer until it reaches