HEAD MEASUREMENTS IN THE WATER FLUTe SYSTEM

The Water FLUTe system described under ground water sampling has three options for measuring the head for the individual ports.

The first method is the direct measurement via the 1/2” tube which extends to the surface for each port. The electric tag line, described in ancillary equipment, is lowered down the tube until it reaches the water level in the tube. This water level can be measured within about 1/8” of the head at the port.

However, because of the check valve in the pumping system, the water level in the 1/2” tube may be higher than the actual head in the formation if the system has not been purged recently. For that reason, it is best to tag the water level after the sampling procedure has purged the water from the pump system. After sampling, the pumping system takes some time to refill. This refill is usually dominated by the formation conductivity for conductivities less than 0.0001cm/sec. Otherwise, the tubing diameter and length will dominate the recharge rate. The water level is best checked at least twice to assure that it is not still rising.

The common slender electric tag lines encounters excessive drag in the 1/2” tube if the water level to be tagged is greater than ~200 ft. below the surface. While the tag line will often drop to lower levels, the retrieval encounters a great deal of drag. It is best to lift the line occasionally while descending to assure that the drag is not too great to allow retrieval. A tag line for use to 500 ft. depths is under development.

Note: If DI water is added to the liner the electric tag line measurement may not work.

A second method of measuring the head is to include a pressure transducer in the system for each port for which a pressure history is desired. The pressure transducer is plumbed into the tube from the port before the tube connects to the pumping system. This is the preferred method for water levels below 200 ft from the surface. For more shallow depths, the hand tag line can be used to calibrate the pressure transducer. Otherwise, the pressure transducer is located on the basis of the as-built dimensions on the tether. The tether is made of a relatively inelastic Spectron material of exceptionally high strength.

A third method of estimating the water level in the tubing is to measure carefully the water expelled during the purge cycle. Since all of the pumping systems for the several ports are located one foot apart on the tether, the relative water volume can be related to the relative water level in the tubes for each port. This technique is the least accurate of the three methods, if the transducer should fail for very deep water tables, this is an option. In this case, the tubing elevation is taken from the as-built dimensions.

The interior water level in the Water FLUTe liner is measured via either a dedicated 1/2” tag line tube located in the tubing bundle, or by using a bubbler tube that is built into the interior of the liner for deep water tables. The bubbler pressure measured, for a small constant air flow rate, is the height of the water in the liner above the bottom end of the bubbler. The bubbler level is provided in the as-built description, but it can be modified in the field during installation. Any modifications must be well noted. For shallow water levels in the liner, a tag line can be lowered into the liner from the surface.

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