PRIVATE WATER SYSTEMS - Design - Casing

Design-Casing

Diameter:

Choosing the right diameter for the well casing and screen is important because it has an affect on both the cost of the well and its efficiency.

For deep wells and wells larger than 4 inches, the diameter is usually chosen to accommodate the size of pump required. The diameter should be 2 nominal sizes larger than the pump to allow sufficient clearance for ease of installation and operation. If the screened interval is to be at much lower depths than the pump, the casing below the pump may be of a smaller diameter. For wells smaller than 4 inches it is satisfactory to select casing which is only 1 size larger than the pump.

In shallow wells where the pump is directly connected to the top of the well casing or connected to a suction pipe inside the well, the casing diameter should be selected in relation to the diameter of the suction inlet of the pump.

Depth:

In general, wells are completed to the bottom of the aquifer. There are two reasons for this. First, more of the aquifer thickness can be used as the intake portion of the well resulting in higher specific capacity. Second, more drawdown can be made available, permitting a greater yield.

One departure from casing to the bottom of the aquifer is when the bottom of the aquifer is known to contain poor quality water. In this case the well should be completed to a depth which will avoid this water.

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