Water in an excavation is not an inconvenience — it is a hazard that can cause trench wall failure, drown a worker, and conceal dangerous utility contacts. The water itself changes the soil classification of the trench walls, requiring a complete re-evaluation of the protective system. On NYC construction sites where the water table can be just a few feet below grade, water in excavations is a daily management challenge.

• No worker may enter an excavation where water has accumulated — the excavation must be pumped down and the CP must re-evaluate the trench before entry
• Water softens cohesive soil and eliminates the cohesion that classifies it as Type B or Type C — the protective system must be redesigned for wet conditions
• Sloping angles must be increased (slopes become less steep) when water is present — Type A dry becomes essentially Type C when saturated
• Dewatering equipment (pump, wellpoints) must be running and monitored continuously when working near the water table

• NYC has a high water table in many areas — Brooklyn, Queens, and lower Manhattan excavations routinely encounter groundwater within 5 feet of grade
• Surface water from rain: even light rain accumulating in a trench changes soil conditions rapidly. Pump out before re-entry; do not simply bail with a bucket
• Water can conceal the bottom of the trench — an apparently shallow puddle may hide a deeper excavation or a damaged pipe
• Waterborne soil transport (boiling): water flowing into the trench bottom can erode soil from beneath the trench walls, causing sudden face failure