How do municipal wastewater treatment plants typically handle stormwater?

Municipal wastewater treatment plants address stormwater management primarily through combined sewer systems or separate systems designed to capture and treat stormwater during rainfall events. In a combined sewer system, both wastewater and stormwater are transported in the same pipes to the treatment facility. During heavy rain, these systems can become overwhelmed, leading to the diversion of excess stormwater directly into nearby water bodies unless mitigated by overflow systems.

In separate systems, stormwater is managed through distinct channels that direct it to different treatment facilities specifically designed for this purpose. This approach helps reduce the burden on wastewater treatment plants and minimizes the risk of pollution from untreated overflow entering local water sources.

The other options do not accurately reflect the established practices in stormwater management. Allowing stormwater to flow directly into rivers and lakes without treatment would pose significant environmental hazards. Relying on evaporation and chemical treatments in open ponds is not a standard practice for large-scale stormwater management in urban areas due to limitations in efficiency and potential chemical impacts. Finally, constructing high walls may mitigate flooding risks but does not address the treatment and management of stormwater, which is crucial in urban planning and environmental safety.