Driven point well driving mechanism - UN FAODriven Point Wells used for Drinking Water
Driven Point Small-Diameter Water Well Installation, Diagnosis & Repair
     


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Driven point well construction, capacities, troubleshooting & repairs: here we define driven point wells & describe how a driven point water well is constructed. We discuss why water flow and pressure are ultimately lost from a driven point well and we explain how to restore water flow (sometimes) without having to construct a new well.

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 Driven Point Wells, Components, Performance, Maintenance

Photograph of sketch of the componentsof a well pit.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. 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.

A 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.

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.

Photograph of sketch of the componentsof a well pit.

Driven point wells consist of a thick-walled metal pipe whose end is shaped into a point and drilled to permit water to enter the pipe. The sketch at left shows two types of driven point well tips or screens - from a small well article provided by the United Nations, FAO.

The driven point is then hammered into the soil, usually to a very shallow depth, perhaps 6' to 8' in depth, and usually in sandy soil or in other soil where a lot of water flows easily to enter the end of the pipe.

The maximum depth for driven point wells is about 80 feet. If local soils are hard or rocky a driven well cannot be used.

The well point may be purchased from a manufacturer (a forged well point) or hand made by cutting and hammering the end of the first pipe section. Holes to permit water entry into the well pipe may be drilled or sawn.

The pointed end of the perforated pipe aids soil penetration and is further protected from soil entry into the pipe itself by a well screen. Additional perforations in the lower length of pipe increase the water intake of the system.

As the UN FAO document explains:

Well screens for driving must have sufficient strength to withstand the forces caused by the driver and the abrasion of the material through which they pass. One common type (Figure 14a above) consists of a perforated drive pipe fitted with a point.

The perforated section of the pipe is wrapped with a layer of brass screen of the desired fineness and the screen is protected from damage by wrapping it with a layer of perforated brass sheet. Both layers are soldered to the pipe.

Another type of well screen (Figure 14b) is manufactured by wrapping trapezoidal rod in a spiral around a set of round longitudinal rods placed in a circular pattern with all intersections welded. This type of screen has the advantage of having a high percentage of open area and a slot shape which cannot become wedged full of fine sand particles.

How are driven point wells installed?

The driven point is then hammered into the soil, usually to a very shallow depth, perhaps 6' to 8' in depth, and usually in sandy soil or in other soil where a lot of water flows easily to enter the end of the pipe.

While special heavy-walled pipe and couplings are needed for the pipe to withstand the forces of being hammered into the ground (usually by a weight that is repeatedly lifted and dropped onto the upper pipe end), driven point wells are often home made or fabricated by a local well driller

The well pipe with attached point and screen is usually driven by a slide hammer much like those used to drive steel fence posts. A larger diameter pipe that will slide over the upper end of the well pipe is raised and dropped repeatedly to drive the well point into the soil. A screw-on pipe cap protects the upper end of the driven well pipe from damage. See the UN FAO sketch of a well driving apparatus (below left).

Alternatively the driving pipe may slide inside the well pipe as shown in our second UN FAO drawing (below-right). Two additional well point driving schemes are included in the illustrations available in the full UN document "Small Diameter Wells", Natural Resources Management & Environment Department, Food and Agriculture Organization of the United Nations, FAO Corporate Document Repository - Self-Help Wells. That excellent resource includes other well boring and drilling methods as well as techniques for dealing with problems such as retrieving broken well pipes or tools dropped into a well. (Local copy provided).

The upper end of the driven point pipe is usually connected to a one line jet pump which "sucks" water out of the ground. In areas of very wet sandy soil a driven point well may be able to produce a barely functional water supply quantity (by modern standards)

Driven point well driving mechanism - UN FAO Driven point well driving mechanism - UN FAO Driven point well driving mechanism - UN FAO Driven point well driving mechanism - UN FAO

Well Water Quantity - Yield of Driven Point Wells

Driven point well water quantity - well yield capacity: Compared with a modern 6" steel casing drilled well, a driven point well installed to the same depth in an aquifer of the same yield capability (the cone of depression is the same), a larger diameter well will yield 1.6 times that of a small diameter well according to United Nations documents on water wells.

Driven point wells often have rapid reduction in water flow rate, depending on the type of soil into which the driven point was inserted. For this reason multiple driven point wells may be connected together to obtain an adequate water supply.

If the water quality from a driven point small diameter well is adequate but the water quantity is not, it may be possible to improve well yield by driving the point deeper into the soil. In general, well yield increases more by increasing well depth than by increasing the well diameter.

Driven point well sanitation and water quality: Even in areas of sandy soils where these shallow wells are frequently used, water quality is questionable as surface contaminants easily enter the water supply, and water quantity is unreliable in areas where the water passage holes in the driven point become easily clogged with debris.

Our clients who have bought homes serviced by a driven point well have ultimately converted to a modern drilled well for better water quantity and for a more sanitary water supply.

Driven point wells are also used in soil de-watering applications during construction and in some locations driven point wells are used to test for water in soils before drilling or digging a higher capacity well.

Restoring the Yield of a Driven Point Well - how can I get my water back?

This topic has moved to DRIVEN POINT WELL RESTORATION.

Small Diameter Jetted Wells or "Wash Wells"

Well Jetting - UN FAO What is a wash well? 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, as suggested by New Hampshire reader Jack Allen.

How are jetted wells or 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 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.

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