In times of heavy rainfall, sanitary sewer systems may overflow, resulting in which overflows?

• A. Storm water overflow
• B. Groundwater leakage
• C. Sanitary sewer overflows (SSOs) and combined sewer overflows (CSOs)
• D. Water treatment bypasses

Answer: (C)

When heavy rainfall pushes a sewer system beyond its capacity, untreated wastewater can escape the system. In sanitary sewer systems, this manifests as sanitary sewer overflows, where sewage spills before it reaches the treatment plant. In areas with a combined sewer system that carries both sanitary waste and stormwater in the same pipes, the extra volume can force a discharge of the mixed wastewater and stormwater—these are known as combined sewer overflows. These overflows are a concern because they release pollutants into waterways during rain events.

Other options don’t fit because stormwater systems overflow are independent of the sanitary network, groundwater leakage is infiltration into pipes rather than an overflow discharge, and water treatment bypasses refer to diverting flow around treatment rather than an actual overflow into the environment.