Select the correct statements used in design and operation of sanitary sewers for municipal systems.

Introduction / Context:
Peaking factors and self-cleansing velocity are basic to sewer design. They determine pipe sizes and slopes that avoid surcharge and sediment deposition.

Given Data / Assumptions:

• Municipal sewer system with diurnal variability.
• Typical peaking factors from empirical curves (e.g., Harmon, Babbit).
• Self-cleansing velocity threshold around 0.6–0.75 m/s (varies with grit).

Concept / Approach:
Designers apply peaking factors to average flows to estimate maximum daily/hourly flows. They also ensure that at minimum flow the velocity exceeds the self-cleansing limit to avoid deposition.

Step-by-Step Solution:
Step 1: Adopt max day ≈ 2 × average day (commonly used planning factor).Step 2: Adopt max hour ≈ 3–6 × average hour (population dependent).Step 3: Provide slopes to keep v ≥ v_self-cleansing at minimum flow.Step 4: Recognize that all three statements are applied together in design.

Verification / Alternative check:
Standard practice manuals and codes show comparable peaking factors and self-cleansing criteria; actual values may be refined by local data.

Why Other Options Are Wrong:

• (a) and (c) only: Omits hourly peaking, which is critical.

Common Pitfalls:
Using a single peaking factor for all sizes; neglecting minimum-velocity checks resulting in chronic silting.

Final Answer:
All of the above