Groundwater measuring point
Groundwater measuring points are set up in order to obtain information on the spatial distribution and temporal variability of the groundwater potential or the pore water pressures in the subsurface. In addition, groundwater measuring points are used to monitor groundwater quality. The measuring points are designed in an open or closed construction, depending on the objective of the investigation.
function
Open groundwater measuring points are used to determine the free groundwater surface in an unconstrained aquifer (ie a groundwater deposit that is not under artesian pressure ) or the groundwater pressure surface in a confined aquifer. In principle, the expansion of the groundwater measuring point corresponds to a verfilterten bore well water extraction, but the tube diameter is selected to be lower, conveyor means such as a submersible motor pump are often introduced only temporarily for the duration of the sampling. Closed groundwater measuring points are used to determine the pore water pressures in the immediate area of the pressure transducer.
Groundwater sampling z. B. for quality monitoring can be carried out at open and closed measuring points.
Establishment of measuring points
The groundwater measuring system and the installation method are to be selected depending on the type and hydraulic permeability of the subsoil (soil or rock), the expected fluctuations, the time resolution of the measurement that is decisive for the respective issue and the planned measurement duration. Specifications for the type and arrangement of groundwater measuring points can be found in the EN 1997-2 standard and in DIN 4049.
To determine the groundwater level, the first step is to measure the difference in height between the measuring point and the groundwater level, referred to as “tapping”, for example using a light plumb line . In order to determine the groundwater level with reference to the geodetic datum of the measuring point, the depth must then be subtracted from the measuring point height. The difference between the groundwater level and the terrain height is known as the floor distance. A groundwater measuring point can also be used to carry out swallowing or pumping tests , with water being introduced in the first case and pumped out in the second. The size of the level rise or lowering funnel determined in this way allows conclusions to be drawn about the hydraulic performance of the aquifer.
In order to prevent the entry of substances harmful to the groundwater directly into the aquifer, groundwater measuring points , like all wells, must be made surface water-tight . This is achieved on the one hand by a corresponding compression between the piping and the existing subsurface above the filter section ("clay barrier"); In order to prevent unauthorized manipulation and vandalism, the observation well is usually secured with a lockable cover ("eg Seba cap").
literature
- Construction and operation of groundwater quality measuring points . In: DVG rules, technical rules worksheet . W 121, July 2003, ISSN 0176-3504 .
- Suitability test of groundwater measuring points . In: DVG rules, technical rules worksheet . W 129, May 2012, ISSN 0176-3504 .
