Groundwater is water held in the spaces between soil particles and in cracks in rock beneath the surface. It collects and moves through water-bearing layers known as aquifers.
Ground conditions affect how easily groundwater moves. Water travels more freely through sand than dense clay, while layered ground can make inflows harder to predict.
On coastal sites, tides can also raise and lower groundwater levels – even when conditions above ground appear unchanged.
Dig below the water table and groundwater can seep into the excavation. Unmanaged inflows can:
Soften the surrounding ground
Affect trench stability
Make the excavation base difficult to compact.
These conditions can slow construction and create additional safety and environmental risks.
The right approach depends on ground conditions, excavation depth and the volume of water coming in.
Wellpointing uses a series of small wells connected to a pump to lower the surrounding groundwater table before water enters the excavation.
Surface dewatering works differently – removing water after it has collected in a trench, pit or other low point.
Tidal groundwater management during dewatering works in New Brighton, Christchurch
Pumped groundwater may carry sediment, hydrocarbons or other contaminants – depending on site conditions.
Settling tanks remove suspended sediment, while other contaminants may need additional treatment. The incoming water quality and discharge requirements determine what treatment the site needs.
At New Brighton, Prime used wellpointing and a settling tank to manage tidally influenced groundwater during pipeline works. The system helped maintain workable trench conditions while treating pumped water before discharge.
Take a closer look at groundwater control on a New Zealand construction site.
Coagulation | Incline Plate Settling | Lamella Clarifier | Settling Tank | Sludge Hopper | Total Suspended Solids | Turbidity