Jetting in Sandy Soil

Jetting in Sandy Soil

One of the simplest forms of applying jetting principles to groundwater work is the jetting of shallow water wells in sandy soil. In its simplest form, a jetting setup for such work, often fabricated by the driller himself, may consist of just a piece of jet pipe connected to the pressure pump or some other water source.

For example, a one inch pipe may be flattened to form a 1/4 inch slot at one end which will produce a high velocity cutting stream of water. The top of the pipe may have a double elbow and union or hose adapter to provide a flexible joint so that the hose may be turned to one side as the jet is lowered into the hole being jetted.

The water source for jetting may be a hand pump or power unit. A suitable amount of water needed to complete the well must be on hand, whether in tanks, drums, or a nearby water source. If the well is being jetted for a potable water supply, the water supply used for the jetting should have at least 50 parts per million (ppm) of chlorine.

This is needed because during jetting, some of the water will enter the sands and water stratum and if it isn't pure, it may contaminate the water well supply you're trying to reach.

Jetting in sand is accomplished in the following manner. A post hole digger is used to start the hole and is dug approximately three feet deep. The jet pipe is raised in a vertical position over the hole. The water pressure is applied and the jet pipe begins cutting the formation and also washes the loosened earth up and over the sides of the hole.

The jet is raised and lowered in a churning, up and down motion, lowering the jet pipe deeper and deeper until the desired depth is reached. The operator watches the materials washed up from the drill hole so that he can determine where the best sands or porous materials are located.

If this depth is not known before jetting, it may be advisable to make a test drill hole a few feet away to determine the proper depth to place the well screen. The actual jetting operation usually requires just a few minutes, so the well pipe and screen assembly must be prepared in advance.

When the driller has reached the proper depth, the well pipe, which is going down into the hole, must be standing by, ready to be placed into the hole. The water pressure is maintained while the driller raises the jetting pipe to the surface.

The hole must be kept full of water until the well pipe is placed. As the retracting jet pipe reaches the top of the hole, the jet water flow is maintained until the well pipe is in position. The water is then shut off and the well pipe is lowered into place, and kept in proper elevation until the sands close around it.

If the sands cave in when the jet pipe is raised and the well strainer is stopped before reaching the desired depth, it may be necessary to place the jet by the side of the well pipe, and lower it until it is about even with the bottom of the screen.

The cutting action of the jet will wash out the sands under the screen. In addition, turning the well pipe with a wrench will help seat the pipe in the sand. If this fails, the well pipe may have to be driven into position with a drive hammer or perhaps the hole will have to be started all over again.