In a combined sewer system, “dry weather flow” (DWF) is understood to mean which of the following?

Introduction / Context:
Combined systems convey sanitary (domestic + industrial) wastewater and storm runoff in the same conduit. However, design and operation often differentiate dry-weather conditions from wet-weather events for capacity, storage, and treatment decisions.

Given Data / Assumptions:

• Combined sewer with separate hydraulic regimes for dry and wet weather.
• No storm precipitation during “dry weather.”
• Continuous domestic and industrial discharges exist regardless of rainfall.

Concept / Approach:

Dry Weather Flow (DWF) includes sanitary flows—domestic and industrial—and excludes storm water. During rainfall, additional inflow/infiltration and surface runoff create Wet Weather Flow (WWF), which can be many times higher than DWF.

Step-by-Step Solution:

Verification / Alternative check:

Flow monitoring during non-rain periods reflects DWF; hydrographs spike during storms, distinguishing WWF from DWF.

Why Other Options Are Wrong:

(a) and (b) are partial; (c) is specifically excluded by definition of DWF.

Common Pitfalls:

Ignoring groundwater infiltration as part of base sanitary flow estimate; confusing combined and separate systems terminology.

Final Answer:

Domestic and industrial sewage together, excluding storm water