Quality assurance tests for newly laid sewer lines: which combination correctly describes common tests carried out on site?

Introduction / Context:
Commissioning sewer lines requires simple but effective field tests to ensure structural integrity, alignment, and freedom from blockages. These tests avoid early failures and maintenance complaints after backfilling and road restoration.

Given Data / Assumptions:

• Newly laid gravity sewers of typical municipal sizes.
• Standard field equipment available: plugs, lamps, mirrors, test balls.
• Need to verify joints, alignment, and clear bore.

Concept / Approach:

The water test checks leakage by plugging ends and observing loss of head or visible leakage. The straightness test confirms alignment by checking a continuous line of sight with a lamp and mirror. The obstruction test verifies no sags or debris by ensuring a ball of specified size passes through freely.

Step-by-Step Solution:

Verification / Alternative check:

Public works manuals outline these as standard acceptance tests before handover.

Why Other Options Are Wrong:

Limiting to only (a) and (b) would omit the crucial obstruction check; hence (d) is most complete.

Common Pitfalls:

Using undersized balls that miss partial blockages; performing tests before adequate curing/backfill support; not documenting test conditions.

Final Answer:

All the above.