Water, Dewatering & Pumps in Excavations

Water is one of the main causes of trench collapses. It adds weight to the soil, washes out the base of the walls, and turns stable clay into mud. Workers can also drown in a trench that floods quickly.

• Construction
• Utility contractors

The rule

Workers can’t work in excavations where water is collecting or has collected unless precautions protect them, such as special support or shield systems, water removal equipment, or safety harnesses and lifelines. A competent person must monitor any water removal.

How water causes collapses

• Saturated soil weighs more and pushes harder on walls and shoring.
• Seeping water carries soil out from the bottom of the wall (undermining).
• Sand and silt can “boil” up from the bottom when groundwater pushes in.
• Soil with seeping water is generally Type C. See Soil Tests.

Keep water out

• Build berms, ditches or diversion so surface runoff can’t flow into the trench.
• Check the forecast and plan to shut down or protect the trench before heavy rain.
• Use well points or deep wells designed by an engineer where groundwater is high.
• Watch for broken water mains and leaking lines nearby.

Pumps

• Gas-powered pumps stay outside the trench and away from the edge; their exhaust (carbon monoxide) can settle into the trench
• Electric submersible pumps plugged into GFCI-protected outlets, with cords protected from damage
• Pump discharge directed away from the trench and handled per stormwater and discharge rules
• Hoses and cords out of walkways and away from the edge
• Pumping monitored by the competent person; trench re-inspected if water rises

See Carbon Monoxide and GFCIs.

Last updated: October 2, 2026