|WORLD METEOROLOGICAL ORGANIZATION||
|Explanation of the criteria for classification and numbering of components||
|Explanation of the dates on the component's description|
PERMANENT ELECTRODE SYSTEMS FOR GROUNDWATER QUALITY MONITORING
1. Purpose and Objectives
site, in-the-borehole monitoring of changes in groundwater
system consists of a 26-strand cable, onto which 13 helical
electrode pairs are attached. The permanent electrode array
allows the electrical resistivity of the subsoil to be measured
at minimum seven to maximum thirteen meters depths. Cables of the
required length can be supplied and are installed as soon as the
borehole has been drilled. The electrical resistivity can be
measured in a few minutes, to ascertain the water quality. If no
changes are recorded over time it is safe to assume
resistivity of the subsoil at various depths.
When the formation resistivity is known, the Cl- content can be derived if information on the composition of the formation water is available from analysis of water samples from observation screens. At low Cl- contents (lower than 50 mg/l), chloride is not the only factor determining the resistivity of the formation water. HCO3- and SO2- have their influence too. This influence, however, diminishes with higher chloride contents.
The observations can be converted directly into the degree of change in the chloride content resistivity of the groundwater. This can either be done manually, using a graph, or with a computer program. The resistivity can be converted to chloride content.
graphs is time-consuming if several cables have to be measured
regularly. Therefore a simple computation program has
been developed which uses a formula to automatically compute the
5. Operational Requirements and Restrictions
position of the cable in the borehole is determined
by geophysical well logging. The cable is taped to the deepest
observation screen and built into the borehole together with that
6. Forms of Presentation
devices are available: one digital and one digital with datalogger.
The advantage of the latter is that no mistakes are made
when reading off the value. An Instruction Manual (in English)
for installing and operating the system is available.
7. Operational Experience
version of the system has been launched in 1965. It has
been updated and improved regularly and has been sold all over
8. Originator and Technical Support
of Applied Geoscience, P.O.Box 6012, 2600 JA DELFT,
The Netherlands, Phone: (31 15) 269 69 00, fax: (31 15) 256 48 00
Institute of Applied Geoscience, The Netherlands.
10. Conditions on Use
For sale at commercial rates, depending on length of cable.
|(First entered: 31 JULY 01||
Last updated: 19 JAN 98)