An operator is digging a trench in clay soil known to swell significantly when wet. A heavy rainfall is expected overnight. What proactive measure should be taken to mitigate the risk of trench instability or water accumulation for morning work?

Question: An operator is digging a trench in clay soil known to swell significantly when wet. A heavy rainfall is expected overnight. What proactive measure should be taken to mitigate the risk of trench instability or water accumulation for morning work?

Answer options:

• Ensure a pump is available on site, but wait until morning to check water levels. ✅ Install proper dewatering systems and consider additional shoring or sloping, covering the trench, or backfilling.
• Cover the trench with plywood sheets to prevent water entry.
• Dig deeper than planned to create a sump for water collection.

Correct answer: Install proper dewatering systems and consider additional shoring or sloping, covering the trench, or backfilling.

Explanation: Heavy rainfall in swelling clay soil presents a significant hazard for trench stability and accumulation. Proactive measures such as dewatering, additional shoring, appropriate sloping, or covering the trench, or backfilling if possible, are essential to meet OHS requirements for excavation stability. Ont. Reg. 213/91, Section 229 specifies measures against water accumulation.