During a combined sewer overflow event, the discharge can include untreated wastewater and which of the following?

• A. Pathogens, nutrients, and organic pollutants.
• B. Only rainfall water.
• C. Only industrial chemicals.
• D. Only treated effluent.

Answer: (A)

During a combined sewer overflow, the system is overwhelmed by a large volume of flow, so untreated wastewater is discharged directly into a receiving water, often mixed with stormwater. This overflow carries not just water but the contaminants from the sewer contents and runoff: pathogens from human waste, nutrients such as nitrogen and phosphorus that promote eutrophication, and organic pollutants from household and industrial sources (including detergents, oils, and other biodegradable organics). That combination is why the option that includes pathogens, nutrients, and organic pollutants best describes what can be present during the discharge. The other possibilities don’t fit because rainfall alone would not include sewage contaminants, industrial chemicals alone miss the biological and nutrient load, and treated effluent would imply cleaning that doesn’t happen during an overflow event.