What is the purpose of making the collection system as watertight as possible?

• A. to reduce maintenance requirements
• B. to prevent root intrusion
• C. to prevent excessive inflow and infiltration
• D. to improve odor control

Answer: (C)

The main idea is to minimize inflow and infiltration into the sewer system. Inflow comes from rainwater or runoff entering through improper connections, while infiltration is groundwater seeping in through cracks, joints, or defective structures. If the collection system is as watertight as possible, these extra waters are greatly reduced, so the wastewater treatment and conveyance system carry flows close to what the system is designed to handle under dry conditions. This lowers peak wet-weather flows, reduces the risk of sewer backups and overflows, and cuts pumping and treatment costs. Root intrusion and odor control are related concerns but are not the primary reason for making the system watertight.