DEEP WELL SYSTEMS

Deep well systems consist of one or more individual wells, each of which has its own submersible pump at the bottom of the well. Such systems are particulary suitable where large volumes of water must be where highly permeable sand and gravel permit rapid recharging of ground water from surrounding areas, where the depth of excavation below the water table exceeds the lift capabilities of other dewatering techniques or where above ground apparatus might interfere with construction operations. Normally, individual wells are spaced at distances of as much as 50 feet. But soil conditions and the dewatering plan can cause spacing as close as just a few feet. Individual wells can have capacities from 21 to 3 000 gallons per minute; total systems with capacities as high as 60 000 gallons per minute have been successful. Deep well pumps can lift water 100 feet or more in a single stage. A variation of the typical deep well system is a pressure within an aquifer. Such wells require no pump, the water being forced to the surface by its own pressure. However, a vacuum pump is frequently used to boost flow. Such wells are often sealed to prevent intake of air or water from higher aquifers.

Deep wells can be more expensive to install and maintain, but in many applications they can be the most economical choice. GART - Dewatering engineers will design the most appropriate system for the conditions and submit a competitive price for the job at hand. A typical deep wel consists of a drilled hole within which is a lower screened casing which admits water to the pump; an upper casing which prevents soil from reaching the pump and, within the casing, the pump and its decharge pipe. The discharge pip supports the pump to which it is attached. Electrical wiring for the pump motor runs between the discharge pipe and the casing. The space between the drilled hole and the casing is normally packed with filter material (coarse sand and/or gravel, for example ) to minimise the pumping of solid material from the soil surrounding the well.

DEEP WELLS

Despite their installation cost, in some cases deep wells are indicated because of their efficiency and of their low operation cost compared to multistage well points. The deep wells can be installed from the surface around the construction area. They will lower the water table to 30 m or more in one single stage, with spacing from 6 m. to 30 m. depending on the soil condition. One well comprise the well itself and its casing, the well screen, the sand filter when needed, the pump and the discharging piping. The diameter of the well and the spacing will be determined from soil study and excavation depth according to the volume of water to be removed to achieve a dry and stable excavation bottom.