Equipment for Groundwater Hydrology Field Work

The available equipment for groundwater hydrology field work is used in different projects, like the one in the Maggia Valley (flow meter tests, among others) or on Vulcano Island (temperature- and electrical conductivity profiles, sampling, pumping tests, among others). From April until June it is used throughout for the environmental engineering practicum. Below a picture is shown from one of the afternoons of the environmental engineering practicum. The car and the trailer are also property of the Institute of Hydromechanics and Water Resources (IHW). In addition, a description is given of the most important measurement devices.

Fig.1. Environmental Engineering Practicum 2004; pumping test close to Winterthur. The necessary equipment is transported in the trailer.

Electric contact gauge

One of the basic measurements that a (groundwater) hydrologist takes in the field is the groundwater level. This is done with a so-called electric contact gauge (see Figure 2). The measurement device is let down in a borehole; when the device reaches the groundwater table a light starts to burn. The groundwater level can be read from the cable.

Fig. 2. (left) Electric contact gauge. (right) Detailed picture of the measuring device.

Electric contact gauge with temperature and electrical conductivity measurement (KLL-Q):

This device can also be used as an electric contact gauge, but it is also able to measure the electrical conductivity and the temperature, and normally it is only used for that (see Figure 3). As the device reacts relatively fast, it is suited to construct a vertical profile of the electrical conductivity and the temperature; the device can be moved quite fast through the whole groundwater column. The measured values are displayed immediately.

An example of a temperature and electrical conductivity profile is given in Figure 4. It has been measured in an area close to the sea water, with volcanic activity, and high groundwater temperatures. In this area measuring the groundwater temperature and electrical conductivity has a special relevance because heat and density transport are to be simulated here.

Fig. 3. SEBA device, that is used to measure temperature and electrical conductivity.

Fig. 4. Temperature and electrical conductivity profile measured at the Vulcano Island, Italy.

DIVER devices (van Essen instruments):

These devices can be programmed with the software Enviromon to measure the electrical conductivity, temperature and pressure. A normal configuration is that one device (DI 250) measures the air pressure and (air) temperature, and another device (DI 218/19 or DI 221/22) the total pressure, electrical conductivity and (water) temperature (see Figure 5). From the measurements with the two devices the height of the water column can be calculated, from which the piezometric level can be obtained.

Fig. 5. (left) The device DI 250 that measures temperature and pressure of air. (right) The device DI 218/19 that measures temperature, electrical conductivity and total pressure of water.

The data are gathered off-line and a measurement campaign can be programmed. It is not possible to read the data instantaneous. A maximum of 16,000 data can be stored; if we would measure each hour, the device can store data during 667 days, without the need to download the data in-between. As an example, the fluctuations in the piezometric level from June 2003 until March 2004 are given (see Figure 6). The DIVER devices cannot display the measured values on a display like the KLL-Q, but their advantage is then that they can store the measured data in the memory, so that a temporal series can be built.

Fig. 6. (above) Precipitation measured in Zürich. (below) Changes in the piezometric level as observed with the DIVER devices, in the period June 2003-March 2004. One can see from the Figure that the piezometric level decreased strongly in the summer of 2003 due to the large evapotranspiration that overcompensated the precipitation. In autumn the piezometric level decreased further, due to the fact (most probably) that the upper soil was dried out. It took until January before a significant recharge event occurred.

Keller devices:

These devices are comparable to the DIVER devices, see Figure 7. However, the newest Keller devices that are in property of IHW can be programmed, and at the same time the measured values can be read and displayed on a computer. The devices can measure in time intervals smaller than one second, and are therefore very suited to be used in pumping tests. Therefore, these devices combine the strong points of the KLL-Q and the Diver devices.

Fig. 7. (left) The Keller device that measures temperature and total pressure. (right) The measured data are displayed on a laptop by means of a software that reads the data from the measurement device.

MP1 Grundfos pump:

Two MP1 pumps are in property of IHW-ETHZ. They are used mainly for groundwater sampling, and seldom for a pumping test, due to the fact that the amount of water that can be pumped is rather limited. In the environmental engineering practicum, the pumps are used in a dual pumping test to obtain a vertical profile of the distribution of the nitrate concentration.

Fig. 8. (left) One of the MP1 Grundfos pumps. (right) The frequency modulator for the MP1 pump.

This pump is designed for the purging and sampling of contaminated groundwater in boreholes with an inside diameter of at least 50 mm. The pump is powered via an adjustable converter BTI/MP1 in the 50 to 400 Hz frequency range. At 400 Hz, the pump provides a flow rate of about 30 l/min in the experiments we performed, where water is pumped from 15 to 30 metres depth. See Figure 8.

Grundfos SP 14A-7:

The Grundfos SP 14A-7 is able to pump up to 20 m3/h. This is considerably more than the MP1 Grundfos pumps, and therefore this pump is used for pumping tests, so that a larger drawdown can be obtained. When pumping tests are carried out, the drawdown is also observed in a borehole close to the well. With a pumping test the hydraulic conductivity and storativity around the pumping well can be estimated. See Figure 9.

Fig. 9. (left) The Grundfos SP 14A-7 pump. (right) The set-up for a pumping test (environmental engineering practicum 2002).

Measuring the pumping rate:

In case of a pumping test, also the pumped quantity of water has to be measured. The device that measures this (Aquaflux 010k/0/6) is shown below, in Figure 10.

Fig. 10. The device that measures the amount of water that is pumped in a certain time.

Flowmeter:

IHW has a Haferland flow meter device. With the flowmeter a vertical profile of the flow velocities can be obtained. These velocities give a qualitative picture, for example from the flow direction (upwards or downwards). The equipment consists of a flow meter (see Figure 11), that is connected with a counter (see Figure 12). This counter displays the depth of the flow meter device. The counter, on its turn, is connected to a PC at which the flow velocities are, instantaneous, displayed as a function of depth. A file is built that contains information on the flow velocities as function of the depth.

Fig. 11. (left) The flowmeter (right) Detailed picture of the flowmeter with the propellers.

Fig. 12. (left) The cable that is used to hang the flow meter in the borehole, and that is connected with a counter that displays the depth of the flow meter device. This equipment is connected to a PC, where among others, the flow velocity and depth are displayed on the computer screen. (right) A flow meter test in the environmental engineering practicum of 2004.

If two velocity profiles are obtained, one without pumping and one with pumping, a vertical profile of hydraulic conductivities can be estimated. Therefore a flowmeter test is normally carried out for both natural flow conditions and stressed conditions (pumping). Figure 13 shows a velocity profile obtained in natural flow conditions.

Fig. 13. Vertical profile of groundwater velocity, in natural condition, measured at a borehole in the municipality of Glattfelden. The groundwater velocity profile has been measured twice.
Stream velocity

The stream velocity is measured with a SEBA Miniflügel M I. The stream velocity can be obtained by means of conversion tables that relate the Schaufeldrehzahl and the stream velocity.

Fig. 14. (left) The device that measures the stream velocity. (right) A measurement in the field, in a stream called Witibach in the municipality of Grenchen (Kanton Solothurn, Switzerland).