Water supply boreholes

Water lowering systems

Water supply boreholes for residential and industrial water supply.

Construction and equipment of boreholes, and water supply tube wells with diameter up to Ø500mm and depth up to 500m.

Rotary drilling with water clay washing with three-roll chisels from Ø59 to Ø500mm diameter.

Air drilling up to Ø315 diameter.

Casing with PVC drill pipes with diameters Ø125, Ø140, Ø160, Ø180, Ø200, Ø250, Ø315 and Ø400 of VALPLAST /Romania/. Felt backfilling in the casing space and water extraction with compressor and airlift.

Water boreholes are vertical holes or shafts drilled in the ground to bring groundwater to the surface. Sometimes wells also serve other purposes, such as exploration and monitoring, artificial recharge, and wastewater discharge. There are many methods of good construction; the choice of a particular method depends on the purpose of the well, the quantity of water required, the depth of groundwater, geological conditions and economic factors. Pipe wells are drilled by rotary or percussion, while shaft wells are dug. Attention to proper design can ensure efficient and long-lasting wells. Once a well is drilled, it must be completed and developed for optimum yield and then tested. Wells should be sealed against the ingress of surface contamination and periodically maintained. Horizontal boreholes are sometimes drilled for special purposes.

It is common practice to drill small-diameter exploratory boreholes that reveal or confirm the presence of groundwater. These are used to clarify the location of the static water level, the water quality and the thickness of the aquifers. Subsequently, if the results are satisfactory, these boreholes are extended to the design diameters and equipped as operational boreholes. Submersible or centrifugal pumps are installed in them, and the mouth is formed with concrete shafts in which shut-off valves and water meters are installed, and pipe connections to water consumers are made. During drilling, it is necessary to clarify and document in detail the lithological varieties and geological layers passed by depth. If necessary, soil samples are taken, recorded and placed in special containers. Subsequently, their grain-size composition or necessary engineering geological indicators can be analysed.

There are different borehole designs, depending on the depth at which the groundwater is located, the water quantities required and the geological conditions. Properly selected design ensures efficient operation of the facilities and ensures their long life.

Once the borehole is constructed, it must be cleaned, equipped and tested. Its effectiveness is evaluated through experimental filtration tests /water drawdowns/ which are carried out for several hours to several days.

The presence of water is mostly related to the lateral inflow that is crossed by the constructed facility. The water level in the boreholes is static and dynamic. Pump depletion results in drawdowns that need to be adjusted to the characteristics of the water body crossed as well as to the local characteristics of the aquifer. Allowable drawdowns shall be fixed for the protection and trouble-free operation of the pumping equipment. The rational use of water resources and the balance of the water body shall be observed on a regional basis.

The hydrogeological conditions in the area need to be clarified to determine the design of the boreholes.

In the design, it is necessary to determine the drilling depth, drilling diameter, operating diameter and casing method.

The depth of the borehole depends on the location and thickness of the aquifer, the type of pumping facilities, in conjunction with the proven flow rate and the dynamic water level.

The initial and final diameter is determined by the flow rates and pumping equipment. The reduction in diameter at depth shall be calculated to accept and pass a specified amount of water.

The operating diameter concerns the part of the borehole into which the pump of a given gauge will be lowered during operation. Depending on the conditions, this depth may be to the filter section or above it.

The boreholes shall be cased with steel or plastic tubing, this includes the filter section and the sediment trap. These activities include the cementing above the filter section to prevent infiltration of surface water or substandard aquifer water.

In selecting the design of boreholes and more specifically the filter section, it is necessary to take into account the chemical composition of the water. The use of different filters depends on the type of water mixture.

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