Well Jetting - UN FAOWash Wells for Drinking Water
Wash Well Construction Methods, Yield Problems & Repair Advice
     


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This article explains wash wells, how awash well is constructed, what are the capacities of a wash well, and how is a wash well water flow problem diagnosed & restored. Small diameter wash wells can provide water sources when water is close to the ground surface and a well pipe or point can be driven into the soil mechanically or by using hydrojetting.

This article series explains installing, diagnosing, and repairing small diameter water wells including driven point wells, wash wells, and jetted wells, three types of water sources that may be used where water is close to the ground surface and a well pipe or point can be driven into the soil mechanically or by using hydrojetting. We include an excellent UN FAO small diameter well document reference that will be helpful to those needing to construct a water well in areas where water is close to the ground surface and money or other resources are limited.

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Small Diameter Wash Wells

Well Jetting - UN FAO

What is a wash well? wash wells, also referred to as JETTED WELLS are similar to driven point wells in that a pipe is forced into the soil and connected (most often) to a single line jet pump. In some communities the term "wash well" is used for this water source in stead of jetted well, as suggested by New Hampshire reader Jack Allen.

How are wash wells installed? In either case, the pipe that is to be used to obtain water is forced into the soil using water at high pressure (40 psi for sandy soils, up to 150 psi for clay or gravel) from an existing water source.

The illustration (left) is from UN document "Small Diameter Wells"

Unlike a driven point well, however, the pipe used in combination with water to force an opening into the ground (the jetting tube) may be a temporary one (the jetting casing is removed from the ground after the jetting process is complete, followed by the insertion of a new casing and casing end screen) or it may be permanent (left in the ground at the end of the jetting process, jacked up just enough to accommodate a well screen lowered inside the casing to its bottom end).

An alternative wash well process permits soil material to actually be removed from the well opening during the jetting process (soil flows up from the bottom of the jetting casing around its outside surface.

Water flowing from the tip of the jet dislocates soil sufficiently to permit the well pipe to be pushed into the ground. Using this process a wash well (or jetted well) may be driven deeper into the soil than a driven point well, and a wash well may be driven through soils harder than those penetrated by a driven point well.

Check valves or foot valves in wash wells: To avoid losing prime in a wash well a check valve may be used at the lower end of the casing, above the well screen. This detail is important for a homeowner to know, because if a wash well or wash well stops working the problem could be a failed check valve (or foot valve) rather than a loss of water in the aquifer.

wash well water capacity or well yield: In soils that contain large amounts of water, particularly in areas of gravel or sand, a wash well (or jetted well or a driven point well) may deliver good water flow or quantity.

wash well water sanitation: However the water quality questions that apply to a driven point well might need to be considered for a wash well too: a well of this design has little protection from unsanitary groundwater compared with a steel-casing drilled-well that is cut into water bearing rock and that is sealed against surface water entry. We suspect that a wash well installed using the alternative process that actually removes material from the well opening by flowing soil to the surface along the outside of the well casing may be more prone to surface water leaking into the well and its aquifer.

Mr. Allen points out that when well repair or service is required for a wash well, the homeowner will need to contact a company who is familiar with this particular well type.

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