Photograph of sketch of the componentsof a well pit. Jetted Wells used for Drinking Water
Jetted Well Problems & Repair Advice
     


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This article explains jetted wells, how a jetted well is constructed, what are the capacities of a jetted well, and how is a jetted well water flow problem diagnosed & restored. These small diameter jetted water 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 describes various types of drinking water sources like wells, cisterns, dug wells, drilled wells, artesian wells and well and water pump equipment.

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 Jetted Wells

Well Jetting - UN FAOA variety of methods are used to install small-diameter water wells in areas where an adequate water supply is sufficiently close to the surface, where cost must be minimized, where well installation speed is important, and where there may be less concern for drinking water contamination from surface runoff. This article describes the two most common small diameter well methods, driven point wells and jetted wells.

We provide advice about what to do when things go wrong. Readers of this document should also see Water Tank Types and before assuming that a water problem is due to the well itself, see WATER PUMP REPAIR GUIDE an specific case which offers an example of diagnosis of loss of water pressure, loss of water, and analyzes the actual repair cost.

The page top sketch shows one of the methods used to construct a wash well or jetted well, described in an excellent UN FAO small diameter well document (reference included here) 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.

Other small diameter well types include bored or augured wells, hydraulic percussion wells, cable tool percussion wells, bail down wells, and hydraulic rotary-drilled wells. All of these small diameter well methods have the advantage of comparatively low cost, rapid installation, and simplicity, and the risk of limited water availability and surface runoff contamination of the aquifer - considerations we explain in more detail below.

What is a jetted well? Jetted wells or WASH WELLS for drinking water supply 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 WELLS is used to mean the same thing as a jetted well water source, as suggested by New Hampshire reader Jack Allen.

How are jetted 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 jetted 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 jetted well (or wash well) may be driven deeper into the soil than a driven point well, and a jetted well may be driven through soils harder than those penetrated by a driven point well.

Check valves or foot valves in jetted wells: To avoid losing prime in a jetted 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 jetted 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.

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

Jetted well water sanitation: However the water quality questions that apply to a driven point well might need to be considered for a jetted 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 jetted 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 jetted well, the homeowner will need to contact a company who is familiar with this particular well type.

The UN FAOdocument describes the jetted or wash well construction process in more detail. Quoting from FAO's description of two jetted or wash well construction methods (see the sketches in this document)

(1) Water is pumped down a jetting tube or pipe which is used inside a temporary or permanent casing (Figure 16a). The excavation of material by the stream of water allows the casing to descend and the excavated material is carried upward out of the well via the annular space between the jetting tube and the casing. Rotating the casing and cutting teeth on its bottom edge increases the rate of descent.

If the casing sunk during the jetting operation is temporary, the final casing with screen attached is lowered inside the temporary casing, which is then jacked out of the hole. Alternatively, the permanent casing may be sunk during the jetting operation. In this case, the well screen is lowered inside the casing and the casing is then jacked up far enough to expose the well screen to the aquifer.

(2) Jetting may be done by pumping the water down through the casing itself with the excavated material being carried up through an annular space around the outside of the casing (Figure 16b). If jetting is interrupted before the casing is sunk to the full desired depth, so that the suspended material settles around it, difficulty may be experienced in re-starting the jetting process.

When an open-ended casing is used, a well screen is subsequently lowered and the casing raised slightly to expose the well screen. A

alternatively a string of casing with a special self-jetting point on the end of a well screen may be used. The jetting orifice at the end of the well screen is closed by a check valve which is held against its seat either by buoyancy or by a spring when not held open by the pressure of the jetting water.

In some cases a smaller string of pipe passes down through the inside of the casing and screen and is screwed into the top of the jetting point. The pipe is used to transmit the jetting water from the pump to the point, without leakage out through the screen. After the jetting operation, this pipe is unscrewed and removed.

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