The design discharge for the combined sewer system shall be taken as A. Equal to rainfall B. Rainfall + DWF C. Rainfall + 2 DWF D. Rainfall + 6 DWF

Equal to rainfall
Rainfall + DWF
Rainfall + 2 DWF
Rainfall + 6 DWF

The correct answer is: C. Rainfall + 2 DWF

The design discharge for a combined sewer system is the maximum flow that the system must be able to handle during a storm event. This flow is calculated by adding the dry weather flow (DWF) to the runoff from rainfall. The DWF is the average flow that the system must be able to handle during non-storm conditions. The runoff from rainfall is the amount of water that flows into the system from the streets and other impervious surfaces during a storm event.

The design discharge is used to size the pipes and other components of the combined sewer system. The system must be able to handle the design discharge without overflowing or backing up.

Option A is incorrect because the design discharge is not equal to the rainfall. The design discharge is greater than the rainfall because it includes the DWF.

Option B is incorrect because the design discharge is not equal to the rainfall plus DWF. The design discharge is greater than the rainfall plus DWF because it includes the runoff from rainfall.

Option D is incorrect because the design discharge is not equal to the rainfall plus 6 DWF. The design discharge is greater than the rainfall plus 6 DWF because it includes the runoff from rainfall.

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